Delinquency Statistics of Commercial Real Estate Loan (Detail) - USD ($) $ in Thousands		Dec. 31, 2016		Dec. 31, 2015
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		$ 1,294,874		$ 1,627,121
Current
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		1,243,160		1,624,710
30 to 59 days
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		50,335
90 days or more
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		1,379		1,163
In foreclosure or bankruptcy proceedings
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total	[1]			1,248
Non-accrual
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		121,038	[2]	35,937	[3]
Commercial Mortgage Loans
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		1,162,233		1,427,328
Commercial Mortgage Loans | Current
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		1,111,898		1,427,328
Commercial Mortgage Loans | 30 to 59 days
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		50,335
Commercial Mortgage Loans | Non-accrual
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		113,509	[2]	15,645	[3]
Mezzanine Loans
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		89,811		169,556
Mezzanine Loans | Current
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		88,432		167,145
Mezzanine Loans | 90 days or more
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		1,379		1,163
Mezzanine Loans | In foreclosure or bankruptcy proceedings
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total	[1]			1,248
Mezzanine Loans | Non-accrual
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		1,379	[2]	12,346	[3]
Preferred Equity Interests
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		42,830		30,237
Preferred Equity Interests | Current
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		42,830		30,237
Preferred Equity Interests | Non-accrual
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		$ 6,150	[2]	$ 7,946	[3]

[1] These loans were on non-accrual due to uncertainty over whether we will fully collect principal and interest.

[2] Includes five loans that are current and one loan that is 30 to 59 days past due in accordance with their terms, but are on non-accrual due to uncertainty over whether we will fully collect principal and interest.

[3] Includes six loans that were current in accordance with their terms, but are on non-accrual due to uncertainty over whether we will fully collect principal and interest.