Shareholders' Equity	3 Months Ended
Shareholders' Equity	Mar. 31, 2012
Shareholders' Equity [Abstract]
Shareholders' Equity	NOTE 8: SHAREHOLDERS' EQUITY *Dividends* In November 2010, the Company obtained waivers from its lenders (Societe Generale, SunTrust Bank and CIT Lending Services Corporation) to permit a $5.00 per share dividend. On November 23, 2010, the Company announced that its Board of Directors declared a special one-time cash dividend of $5.00 per share on its Common Stock (the "Special Cash Dividend"). The Special Cash Dividend was paid on December 27, 2010 to the stockholders of record at the close of business on December 6, 2010. The aggregate amount of the payment made in connection with the Special Cash Dividend was approximately $129.0. On December 20, 2010, the Company's Board of Directors granted restricted stock units (the "RSU Dividend") to holders of unvested restricted stock units on the record date of the Special Cash Dividend in order to provide these holders with an amount that approximated the value of the Special Cash Dividend. In total, the Company granted 40,508 restricted stock units pursuant to the RSU Dividend, of which up to 1,246 restricted stock units vested in February 2011 based upon the achievement of certain performance targets established for fiscal year 2010, 28,656 restricted stock units are scheduled to vest on November 15, 2011, 9,360 are scheduled to vest November 16, 2011 and up to 1,246 restricted stock units are scheduled to vest on or before March 15, 2012 based upon the achievement of certain performance targets established for fiscal year 2011. Additionally, on December 20, 2010, the Company's Board of Directors granted shares of Common Stock (the "Option Dividend") to holders of vested unexercised options to purchase shares of Common Stock in order to provide these holders with an amount that approximated the value of the Special Cash Dividend. On December 27, 2010, the Company delivered 9,281 shares of Common Stock pursuant to the Option Dividend. Additionally, the Company paid cash to one former employee and to the estate of one deceased employee totaling $0.007. In the fourth quarter of 2010, the Company recorded stock-based compensation expense of $0.5 in connection with the Option Dividend. *Stock Split* On August 3, 2009, the Board of Directors of the Company authorized a two-for-one Common Stock split, effected in the form of a 100% stock dividend, which was distributed on September 3, 2009. Each shareholder of record on August 20, 2009 received one additional share of Common Stock for each share of Common Stock held on that date. All share and per share information for prior periods, including warrants, options to purchase shares of Common Stock, restricted stock units, warrant and option exercise prices, shares reserved under the 2003 Plan and the 2008 Plan, weighted average fair value of options granted, Common Stock and additional paid-in capital accounts on the consolidated balance sheets and consolidated statement of shareholders' equity, have been retroactively adjusted, where applicable, to reflect the two-for-one stock split. *Amendment to the Company's Amended and Restated Certificate of Incorporation* On June 24, 2010, the Company's stockholders approved an amendment to the Company's Amended and Restated Certificate of Incorporation (the "Amendment") to increase the number of authorized shares of its Common Stock from 30 million to 200 million. The number of authorized shares of preferred stock remained at 10 million. The increase in the number of the Company's authorized shares of Common Stock could have an anti-takeover effect by discouraging or hindering efforts to acquire control of the Company. The Company would be able to use the additional shares to oppose a hostile takeover attempt or delay or prevent changes in control or management of the Company. This was not the intent of the Board of Directors in adopting the Amendment, nor has the Amendment been adopted in response to any known threat to acquire control of the Company. The increase in the authorized shares of Common Stock became effective upon the filing of the Amendment with the Secretary of State of the State of Delaware on June 24, 2010. *Rights Agreement* On August 3, 2006, the Company entered into a Rights Agreement (the "Rights Agreement") with American Stock Transfer & Trust Company, as rights agent, which was amended and restated on August 3, 2009 and subsequently amended as of January 26, 2010 and March 18, 2012 (as amended, the "Amended and Restated Rights Agreement"). The Amended and Restated Rights Agreement was ratified by the Company's stockholders at its annual meeting on June 24, 2010. As a result, the Rights (as defined below) under the Amended and Restated Rights Agreement will remain in effect until August 7, 2012, unless sooner terminated by the Company's Board of Directors. The following description of the Amended and Restated Rights Agreement does not purport to be complete and is qualified in its entirety by reference to the Amended and Restated Rights Agreement included as Exhibit 4.1 to the Company's Current Report on Form 8-K filed with the SEC on August 3, 2009, the Amendment to Amended and Restated Rights Agreement, dated as of January 26, 2010, between AboveNet, Inc. and American Stock Transfer & Trust Company, LLC included as Exhibit 4.1 to the Company's Current Report on Form 8-K filed with the SEC on January 28, 2010 and the Second Amendment to the Amended and Restated Rights Agreement, dated as of March 18, 2012, between AboveNet, Inc. and American Stock Transfer & Trust Company, LLC included as Exhibit 4.6 to the Company's Current Report on Form 8-K filed with the SEC on March 19, 2012. In connection with the initial Rights Agreement, the Company's Board of Directors declared a dividend distribution of one preferred share purchase right (a "Right") for each then outstanding share of Common Stock. The dividend was paid on August 7, 2006 to the stockholders of record on that date. Until the earlier to occur of (i) the date that is 10 days following the date of a public announcement that a person, entity or group of affiliated or associated persons have acquired beneficial ownership of 15% or more of the outstanding shares of Common Stock (an "Acquiring Person") or (ii) 10 business days (or such later date as may be determined by action of the Company's Board of Directors prior to such time as any person or entity becomes an Acquiring Person) following the commencement of, or announcement of an intention to commence, a tender offer or exchange offer the consummation of which would result in any person or entity becoming an Acquiring Person (the earlier of such dates being called the "Distribution Date"), the Rights will be evidenced by the Common Stock certificates or book-entry shares. The Rights are not exercisable until the Distribution Date. Each Right, upon becoming exercisable, will entitle the holder to purchase from the Company a specified fraction of a share of the Company's Series A Junior Participating Preferred Stock (the "Preferred Shares") at the then effective purchase price. The Rights will expire on August 7, 2012, unless earlier redeemed or exchanged. The number of outstanding Rights and the number of Preferred Shares issuable upon exercise of the Rights are also subject to adjustment in the event of a stock split of the Common Stock or a stock dividend on the Common Stock payable in Common Stock or subdivisions, consolidation or combinations of the Common Stock occurring, in any case, prior to the Distribution Date. The purchase price payable and the number of Preferred Shares or other securities or other property issuable upon exercise of the Rights are subject to adjustment from time to time to prevent dilution as described in the Amended and Restated Rights Agreement. As a result of the Company's stock split discussed above, appropriate adjustments under the Amended and Restated Rights Agreement have been made. In the event that any person or group of affiliated or associated persons becomes an Acquiring Person, proper provision will be made so that each holder of a Right, other than Rights beneficially owned by the Acquiring Person and its associates and affiliates (which will thereafter be void), will have the right to receive upon exercise, in lieu of Preferred Shares, that number of shares of Common Stock having a market value of two times the then effective exercise price of the Right (or, if such number of shares is not and cannot be authorized, the Company may issue Preferred Shares, cash, debt, stock or a combination thereof in exchange for the Rights). In the event that the Company is acquired in a merger or other business combination transaction or 50% or more of its consolidated assets or earning power are sold to an Acquiring Person, its associates or affiliates or certain other persons, proper provision will be made so that each holder of a Right, other than Rights beneficially owned by the Acquiring Person and its associates and affiliates (which will thereafter be void), will thereafter have the right to receive, upon the exercise thereof at the then current exercise price of the Right, in lieu of Preferred Shares, that number of shares of Common Stock of the acquiring company which at the time of such transaction will have a market value of two times the then effective exercise price per Right. At any time after a person becomes an Acquiring Person and prior to the acquisition by such Acquiring Person of 50% or more of the outstanding shares of Common Stock, the Company may exchange the Rights (other than Rights owned by such Acquiring Person or group which have become void), in whole or in part, at an exchange ratio of one share of Common Stock per Right (or, at the election of the Company, the Company may issue cash, debt, stock or a combination thereof in exchange for the Rights), subject to adjustment. At any time prior to the earlier of (i) such time that a person has become an Acquiring Person or (ii) the final expiration date, the Company may redeem all, but not less than all, of the outstanding Rights at a price of $0.005 per Right (the "Redemption Price"). The Rights may also be redeemed at certain other times as described in the Amended and Restated Rights Agreement. Immediately upon any redemption of the Rights, the right to exercise the Rights will terminate and the only right of the holders of Rights will be to receive the Redemption Price. The terms of the Rights may be amended by the Company's Board of Directors without the consent of the holders of the Rights, except that from and after such time as the rights are distributed no such amendment may adversely affect the interest of the holders of the Rights other than the interests of an Acquiring Person or its affiliates or associates. Until a Right is exercised, the holder thereof, as such, will have no rights as a stockholder of the Company, including, without limitation, the right to vote or to receive dividends. The March 18, 2012 amendment to the Rights Agreement permits the execution of the Merger Agreement (as such term is defined in Note 14, "Merger Agreement with Zayo Group, LLC," below) and the performance and consummation of the transactions contemplated by the Merger Agreement, including the Merger (as such term is defined in Note 14, "Merger Agreement with Zayo Group, LLC," below), without triggering the provisions of the Rights Agreement. See Note 14, "Merger Agreement with Zayo Group, LLC." *Repurchase Program* On December 7, 2011, the Board of Directors of the Company authorized a share repurchase program of up to $200.0 of the Common Stock through December 31, 2012 (the "Repurchase Program"). The Board also authorized management to enter into one or more prearranged stock repurchase plans under Rule 10b5-1 of the Securities Act of 1934 in connection with the Repurchase Program. Through March 31, 2012, the Company purchased 41,157 shares pursuant to the Repurchase Program at a cost of $2.7, of which 11,700 shares were purchased during the three months ended March 31, 2012 at an aggregate cost of $0.8. *2010 Employee Stock Purchase Plan* On June 24, 2010, the Company's stockholders approved the AboveNet, Inc. 2010 Employee Stock Purchase Plan, which was adopted by the Board of Directors on April 28, 2010 (as amended, the "Stock Purchase Plan"). The Stock Purchase Plan is administered by the Compensation Committee of the Board of Directors. The aggregate number of shares of Common Stock that may be issued pursuant to the Stock Purchase Plan is 300,000, subject to increase or decrease by reason of stock splits, reclassifications, stock dividends, or similar corporate events as determined by the Compensation Committee. Eligibility and Participation All employees of the Company, or any of its designated subsidiaries, who have completed at least ninety (90) days of employment on or before the first day of the applicable offering period are eligible to participate in the Stock Purchase Plan, subject to certain limitations imposed by the Internal Revenue Code and certain other limitations set forth in the Stock Purchase Plan. An employee may not participate in the Stock Purchase Plan if, immediately after he or she joined, he or she would own stock and/or hold rights to purchase stock possessing 5% or more of the total combined voting power or value of all classes of stock of the Company or of any subsidiary of the Company. Officers of the Company that are subject to the reporting requirements of Section 16(a) under the Securities Exchange Act of 1934 (the "Exchange Act") are also not eligible to participate. The Stock Purchase Plan also limits an employee's rights to purchase stock under all employee stock purchase plans (those subject to Section 423 of the Internal Revenue Code) of the Company and its subsidiaries so that such rights may not accrue at a rate that exceeds $0.025 of fair market value of such stock (determined as of the first day of the offering period) for each calendar year in which such right to purchase stock is outstanding at any time. In addition, no employee may purchase more than 200 shares of Common Stock under the Stock Purchase Plan in any offering period. Employees may withdraw from the Stock Purchase Plan at any time prior to the end of the then current offering period. As of December 31, 2011, the Company had a total of approximately 700 employees who were eligible to participate in the Stock Purchase Plan. Offering Periods; Purchase Price The Stock Purchase Plan operates by a series of offering periods of approximately 10 months in duration commencing on each January 16 and ending on November 15 (except that the 2010 offering period was from September 1, 2010 to November 15, 2010).The purchases are made for participants at the end of each offering period by applying payroll deductions accumulated over the course of the offering period towards such purchases. The payroll deductions accumulated over the course of the offering period are included in "Accrued expenses" in the Company's consolidated balance sheet. The price at which these purchases will be made will equal 85% of the lesser of the fair market value of the Common Stock as of the first day of the offering period or the fair market value on the last day of the offering period. 2012, 2011 and 2010 Offering Periods 117employees are participating in the January 16, 2012 to November 16, 2012 offering period. Payroll withholdings to make purchases are scheduled to be $0.6 over the 2012 offering period, of which $0.2 was withheld during the three months ended March 31, 2012. 108 employees participated in the January 16, 2011 to November 15, 2011 offering period. Payroll withholdings to make purchases were $0.6 over the 2011 offering period. 86 employees participated in the September 1, 2010 to November 15, 2010 offering pursuant to which $0.2 was withheld over the 2010 offering period. The Company follows FASB Technical Bulletin No. 97-1, "Accounting under Statement 123 for Certain Employee Stock Purchase Plans with a Look-Back Option," (now known as FASB ASC 718) and SFAS No. 123(R) (also now known as FASB ASC 718) to account for the Stock Purchase Plan. Because the Stock Purchase Plan provides for a discount greater than 5%, it is a compensatory plan and qualifies for fair value accounting. Accordingly, the fair market value of the grant is calculated as of the grant date in accordance with SFAS No. 123(R). Additionally, the fair value of the look-back option is calculated on a similar basis. The Company also estimates future forfeitures (withdrawals) from the Stock Purchase Plan as provided under FASB ASC 718. The Company recognized non-cash stock-based compensation expense with respect to the Stock Purchase Plan of $0.03 for each of the three months ended March 31, 2012 and 2011. The Company issued 12,288 shares with respect to the 2011 Offering Period. The Company issued 4,414 shares of Common Stock with respect to the 2010 offering period.

The entire disclosure for shareholders' equity, comprised of portions attributable to the parent entity and noncontrolling interest, if any, including other comprehensive income (as applicable). Including, but not limited to: (1) balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings; (2) accumulated balance for each classification of other comprehensive income and total amount of comprehensive income; (3) amount and nature of changes in separate accounts, including the number of shares authorized and outstanding, number of shares issued upon exercise and conversion, and for other comprehensive income, the adjustments for reclassifications to net income; (4) rights and privileges of each class of stock authorized; (5) basis of treasury stock, if other than cost, and amounts paid and accounting treatment for treasury stock purchased significantly in excess of market; (6) dividends paid or payable per share and in the aggregate for each class of stock for each period presented; (7) dividend restrictions and accumulated preferred dividends in arrears (in aggregate and per share amount); (8) retained earnings appropriations or restrictions, such as dividend restrictions; (9) impact of change in accounting principle, initial adoption of new accounting principle and correction of an error in previously issued financial statements; (10) shares held in trust for Employee Stock Ownership Plan (ESOP); (11) deferred compensation related to issuance of capital stock; (12) note received for issuance of stock; (13) unamortized discount on shares; (14) description, terms, and number of warrants or rights outstanding; (15) shares under subscription and subscription receivables, effective date of new retained earnings after quasi-reorganization and deficit eliminated by quasi-reorganization and, for a period of at least ten years after the effective date, the point in time from which the new retained dates; and (16) retroactive effective of subsequent change in capital structure.

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