Investments in Unconsolidated Entities - Summary of Investments in Unconsolidated Entities (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Schedule of Variable Interest Entities for Loans to Commercial Borrowers [Line Items]
Investment Balance, January 1	$ 537,631	$ 410,062
Contributions	12,793	149,132
Company's Equity in Net Income (including adjustments for basis differences)	2,556	3,590
Other Comprehensive Loss of Unconsolidated Entities	(2,014)	(1,487)
Distributions	(62,970)	(23,666)
Investment Balance, End of Period	$ 487,996	$ 537,631