Derivative Contracts - Effects of Derivative Contracts in Condensed Consolidated Financial Statements (Detail) (USD $) In Thousands, unless otherwise specified			3 Months Ended		6 Months Ended							3 Months Ended		6 Months Ended						3 Months Ended	6 Months Ended			3 Months Ended	6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 cost of sales, overstated/understated amount [Member]	Jun. 30, 2012 cost of sales, overstated/understated amount [Member]	Jun. 30, 2013 cost of sales, overstated/understated amount [Member]	Jun. 30, 2012 cost of sales, overstated/understated amount [Member]	Jun. 30, 2013 Prepaid Expenses and Other Current Assets [Member]	Dec. 31, 2012 Prepaid Expenses and Other Current Assets [Member]	Dec. 31, 2012 Other Noncurrent Assets [Member]	Jun. 30, 2013 Open metal contracts [Member]	Dec. 31, 2012 Open metal contracts [Member]	Jun. 30, 2013 Open metal contracts [Member] cost of sales, overstated/understated amount [Member]	Jun. 30, 2012 Open metal contracts [Member] cost of sales, overstated/understated amount [Member]	Jun. 30, 2013 Open metal contracts [Member] cost of sales, overstated/understated amount [Member]	Jun. 30, 2012 Open metal contracts [Member] cost of sales, overstated/understated amount [Member]	Jun. 30, 2013 Open electricity contracts [Member]	Dec. 31, 2012 Open electricity contracts [Member]	Jun. 30, 2013 Interest rate cap agreements [Member]	Dec. 31, 2012 Interest rate cap agreements [Member]	Jun. 30, 2012 Interest rate cap agreements [Member] Interest Expense [Member]	Jun. 30, 2013 Interest rate cap agreements [Member] Interest Expense [Member]	Jun. 30, 2012 Interest rate cap agreements [Member] Interest Expense [Member]	Dec. 31, 2012 Open natural gas contracts [Member]	Jun. 30, 2012 Natural gas contracts [Member] cost of sales, overstated/understated amount [Member]	Jun. 30, 2013 Natural gas contracts [Member] cost of sales, overstated/understated amount [Member]	Jun. 30, 2012 Natural gas contracts [Member] cost of sales, overstated/understated amount [Member]	Jun. 30, 2013 Electricity contracts [Member] cost of sales, overstated/understated amount [Member]	Jun. 30, 2012 Electricity contracts [Member] cost of sales, overstated/understated amount [Member]	Jun. 30, 2013 Electricity contracts [Member] cost of sales, overstated/understated amount [Member]	Jun. 30, 2012 Electricity contracts [Member] cost of sales, overstated/understated amount [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Assets	$ 2,032	$ 775								$ 1,953	$ 603					$ 79	$ 169		$ 1				$ 2
Gross Amounts Offset in Consolidated Balance Sheet	(1,574)	(226)								(1,574)	(224)						(2)
Net Amounts of Assets Presented in Consolidated Balance Sheet	458	549								379	379					79	167		1				2
Amount Not Offset in the Consolidated Balance Sheet, Financial Instruments
Amount Not Offset in the Consolidated Balance Sheet, Cash Collateral Received
Net Amount	458	549								379	379					79	167		1				2
Derivative Asset	458	549					458	548	1
Gross Amounts of Recognized Liabilities	1,574	226								1,574	224						2
Gross Amounts Offset in Consolidated Balance Sheet	(1,574)	(226)								(1,574)	(224)						(2)
Net Amounts of Liabilities Presented in Consolidated Balance Sheet
Amount Not Offset in the Consolidated Balance Sheet, Financial Instruments
Amount Not Offset in the Consolidated Balance Sheet, Cash Collateral Deposited	267	767
Net Amount
Realized and unrealized gain (loss)			469	(425)	564	538						634	(606)	651	504									34	(2)	69	(165)	147	(85)	(35)
Unrealized loss																				$ (12)	$ (1)	$ (146)