Carrying Value and Estimated Fair Value of Company's Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cash and cash equivalents, at carrying value	$ 108,619	$ 21,568	$ 37,894	$ 129,969
Commercial first mortgage loans, at carrying value	142,921	109,006
Subordinate loans, at carrying value	246,246	149,086
Repurchase agreements, at carrying value	6,598	47,439
TALF borrowings, at carrying value		(251,327)
Borrowings under repurchase agreements, at carrying value	(225,158)	(290,700)
Cash and cash equivalents, estimated fair value	108,619	21,568
Commercial first mortgage loans, estimated fair value	150,144	116,516
Repurchase agreements, estimated fair value	6,598	47,415
TALF borrowings, estimated fair value		(256,171)
Borrowings under repurchase agreements, estimated fair value	(225,158)	(290,700)
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Subordinate loans, estimated fair	$ 250,520	$ 154,778