Lease Obligations - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Operating Leased Assets [Line Items]
Rent expense related to operating leases	$ 1,400,000	$ 1,100,000	$ 1,100,000
Future minimum payments under current lease agreements, year 2013	1,200,000
Future minimum payments under current lease agreements, year 2014	1,200,000
Future minimum payments under current lease agreements, year 2015	794,000
Future minimum payments under current lease agreements, year 2016	793,000
Future minimum payments under current lease agreements, year 2017	420,000
Future minimum payments under current lease agreements, thereafter	3,100,000
Future minimum payments under current lease agreements, total	$ 7,500,000