Credit Facilities - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Jan. 11, 2013	Dec. 31, 2011
Line of Credit Facility [Line Items]
Line of credit	$ 25,000,000	$ 10,000,000
Annual interest rate	1-month London Interbank Offered Rate (“LIBOR”) plus 1.85%
Spread over LIBOR	1.85%
Unused commitment fees	0.25%
Outstanding borrowing under line of credit	0		0
Outstanding letters of credit	$ 1,600,000		$ 2,600,000