Commitments and Contingencies - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Environmental Matters And Other Commitments And Contingencies [Line Items]
Recorded accrual amount	$ 300,000
Upper end of the range of reasonably possible costs	1,700,000
Estimate cost of future remediation	30,000
Estimated cost of future remediation if MSD is not obtained	1,700,000
Lease expense	2,000,000	2,100,000	2,200,000
Oxygen and Nitrogen [Member]
Environmental Matters And Other Commitments And Contingencies [Line Items]
Unconditional facility fee	1,400,000
Purchases made under supply agreement	3,000,000	3,100,000	3,300,000
By-Product Processor [Member]
Environmental Matters And Other Commitments And Contingencies [Line Items]
Purchases made under supply agreement	3,000,000	2,600,000	2,200,000
Aggregate fixed monthly fee	$ 900,000