Roll-Forward of Allowance for Losses for Commercial Mortgages Mezzanine Loans, and Other Loans (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Mortgage Loans on Real Estate [Line Items]
Balance, Beginning of Period	$ 22,955	$ 30,400	$ 46,082
Provision	5,500	3,000	2,000
Charge-offs, net of recoveries	(19,237)	(10,445)	(17,682)
Balance, End of Period	9,218	22,955	30,400
Commercial mortgages
Mortgage Loans on Real Estate [Line Items]
Balance, Beginning of Period			573
Provision	360	344	(539)
Charge-offs, net of recoveries	(360)	(344)	(34)
Mezzanine Loans
Mortgage Loans on Real Estate [Line Items]
Balance, Beginning of Period	21,636	22,819	32,951
Provision	4,894	7,606	7,516
Charge-offs, net of recoveries	(18,638)	(8,789)	(17,648)
Balance, End of Period	7,892	21,636	22,819
Preferred Equity Interests
Mortgage Loans on Real Estate [Line Items]
Balance, Beginning of Period	1,319	7,581	7,142
Provision	246	(4,950)	439
Charge-offs, net of recoveries	(239)	(1,312)
Balance, End of Period	1,326	1,319	7,581
Other loans
Mortgage Loans on Real Estate [Line Items]
Balance, Beginning of Period			5,416
Provision			$ (5,416)