Cash Equivalents And Marketable Securities (Schedule Of Cash Equivalents And Available-For-Sale Marketable Securities Reported At Fair Value) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents	$ 15,907	$ 7,155
Total marketable securities, available-for-sale	4,500	38,081
Total cash equivalents and marketable securities	20,407	45,236
Money Market Mutual Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents	24	6,742
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents	1,240	413
Commercial Paper ST [Member]
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents	11,744
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Total marketable securities, available-for-sale		7,370
Variable Rate Demand Obligation [Member]
Schedule of Available-for-sale Securities [Line Items]
Total marketable securities, available-for-sale	4,000	13,995
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents	500
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total marketable securities, available-for-sale	500	$ 16,716
Debt Securities issued by U.S. Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents	$ 2,399

Lumos Networks Corp. 10-Q