Commercial Mortgage Loan Portfolio (Parenthetical) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012
Mortgage Loans on Real Estate [Line Items]
Senior sub-participation interest in New York, NY Hotel Loan	$ 120,000
Interest rate on New York, NY Hotel Loan	1.72%
Repayment of first mortgage	$ 33,000
Mortgage loan fee percentage	0.50%
Origination fee	1.00%
LIBOR floor	0.50%