Related Party Transactions - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Contran [Member] | Intercorporate Services Agreement [Member]
Related Party Transaction [Line Items]
Related party expense	$ 2.5	$ 2.1	$ 2.1
Contran [Member] | Intercorporate Services Agreement [Member] | Scenario, Forecast [Member]
Related Party Transaction [Line Items]
Related party expense	2.7
Tall Pines Insurance Company and EWI RE, Inc. [Member]
Related Party Transaction [Line Items]
Related party expense	5.4	4.2	3.7
Alter Trading Corporation [Member]
Related Party Transaction [Line Items]
Purchase under scrap supply agreement		285.2	205.9
Payable to related party	0.1
Alter Recycling Company, LLC [Member]
Related Party Transaction [Line Items]
Purchase under scrap supply agreement	$ 263.1	$ 0.8	$ 0.5