Subsequent Event - Additional Information (Detail) (USD $)			1 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Mar. 08, 2013 Subsequent Event Separation Agreement Transactions	Mar. 08, 2013 Subsequent Event Separation Agreement Transactions Maximum	Mar. 08, 2013 Subsequent Event Separation Agreement Transactions Increase Amount After April 12, 2013	Mar. 08, 2013 Subsequent Event Separation Agreement Transactions March 2015	Mar. 08, 2013 Subsequent Event Separation Agreement Transactions March 2016	Feb. 06, 2013 Subsequent Event Merger Agreement
Subsequent Event [Line Items]
Conversion price of common stock under merger agreement								$ 20.65
Lump sum payment of employee base salary per agreement			$ 750,000
Employee annual salary with regular payroll schedule	13,300,000	15,100,000	750,000
Employee payment period with regular payroll schedule			12 months
Employee lump sum payment representing pro-rated bonus amount			307,398		3,014
Employee lump sum payable amount						$ 1,100,000	$ 1,100,000
Employee benefit coverage period at his election				18 months

METALS USA HOLDINGS CORP. 10-K