Property and Equipment - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items]
Depreciation expense	$ 1,482	$ 1,486	$ 1,480
Operating lease agreements expiring date	2027
Rent expense related to leases	$ 1,141	$ 1,152	$ 1,148
Percentage of property leased	26.00%
Springfield [Member]
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items]
Operating lease agreements expiring date	2016