Significant Accounting Policies - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Significant Accounting Policies [Line Items]
Bad debt expense	$ 4,000	$ (99,000)	$ 4,000
Net change in inventory reserves	300,000	148,000	(166,000)
Construction in progress, interest expense capitalized	476,000	394,000
Maintenance expense	17,700,000	15,900,000	11,900,000
Depreciation expense	12,100,000	7,000,000	5,500,000
Business acquisition, purchase price allocation, intangible assets amortization period	5 years
Amortization expense	266,000	100,000
Amortization expense of intangible asset for 2013	266,000
Amortization expense of intangible asset for 2014	266,000
Amortization expense of intangible asset for 2015	266,000
Amortization expense of intangible asset for 2016	166,000
Deferred finance cost amortization expense	308,000	153,000	17,000
North Jackson Facility | Non-compete Agreements
Significant Accounting Policies [Line Items]
Business acquisition, purchase price allocation, intangible assets		$ 1,300,000
Minimum
Significant Accounting Policies [Line Items]
Material major equipment capitalized maintenance cost, amortization period	6 months
Percentage for tax position likely be realized upon settlement	50.00%	50.00%	50.00%
Minimum | Buildings And Land Improvements
Significant Accounting Policies [Line Items]
Property Plant and Equipment,estimated useful lives	10 years
Minimum | Machinery and Equipment
Significant Accounting Policies [Line Items]
Property Plant and Equipment,estimated useful lives	5 years
Maximum
Significant Accounting Policies [Line Items]
Material major equipment capitalized maintenance cost, amortization period	12 months
Maximum | Buildings And Land Improvements
Significant Accounting Policies [Line Items]
Property Plant and Equipment,estimated useful lives	39 years
Maximum | Machinery and Equipment
Significant Accounting Policies [Line Items]
Property Plant and Equipment,estimated useful lives	20 years
Fry Steel Company
Significant Accounting Policies [Line Items]
Concentration of credit risk, percentage of net sales	11.00%	11.00%	8.00%
Concentration of credit risk, percentage of accounts receivable	6.00%	9.00%
Carpenter Technology Corporation
Significant Accounting Policies [Line Items]
Concentration of credit risk, percentage of net sales	10.00%	12.00%	14.00%
Concentration of credit risk, percentage of accounts receivable	6.00%	13.00%