Credit Facilities - Additional Information (Detail) (USD $)	0 Months Ended	12 Months Ended
	Dec. 10, 2010	Dec. 31, 2012	Dec. 14, 2010
Line of Credit Facility [Line Items]
Line of credit, available borrowings			$ 30,000,000
Line of credit, maturity date	Dec. 31, 2012
Line of credit, interest rate description		Libor plus 1.5% to 2.0%
Interest rate on borrowings at LIBOR plus, minimum	1.50%
Interest rate on borrowings at LIBOR plus, maximum	2.00%
Minimum unrestricted cash balance requirement	10,000,000
Unrestricted cash deposit	55,000,000
Line of credit, amount outstanding		$ 0
Minimum
Line of Credit Facility [Line Items]
Line of credit, unused facility fee	0.05%
Maximum
Line of Credit Facility [Line Items]
Line of credit, unused facility fee	0.125%