Commitments and Contingencies - Additional Information (Detail) (USD $)	120 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Commitment And Contingencies [Line Items]
Claims disbursed since inception of insurance company	$ 7,700,000
Insurance reserves	6,600,000	7,200,000
Insurance reserves classified as current accrued liabilities and other	871,000	951,000
Maximum
Commitment And Contingencies [Line Items]
Estimate of the amount of probable loss	13,200,000
Minimum
Commitment And Contingencies [Line Items]
Estimate of the amount of probable loss	$ 5,100,000