Revolving Line of Credit - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Line Of Credit Facility [Abstract]
Line of credit facility, maximum borrowing capacity	$ 50,000,000		$ 50,000,000
Interest rate, description			LIBOR plus 3%
Line of credit facility basis spread on variable rate			3.00%
Line of credit facility, expiration date			Mar. 03, 2014
Line of credit facility extended maturity date			Mar. 03, 2015
Line of credit facility, amount outstanding	0		0		0
Line of credit facility, commitment fee amount	$ 44,000	$ 43,000	$ 87,000	$ 62,000