Derivative Contracts - Effects of Derivative Contracts in Condensed Consolidated Financial Statements (Parenthetical) (Detail)	Jun. 30, 2013 Contract	Dec. 31, 2012 Contract
Open metal contracts [Member]
Derivatives, Fair Value [Line Items]
Number of contracts	334	208
Number of contracts	218	85
Open electricity contracts [Member]
Derivatives, Fair Value [Line Items]
Number of contracts	6	17
Number of contracts		1
Interest rate cap agreements [Member]
Derivatives, Fair Value [Line Items]
Number of contracts	2	2
Open natural gas contracts [Member]
Derivatives, Fair Value [Line Items]
Number of contracts		6