Delinquency Statistics of Commercial Real Estate Loan (Detail) - USD ($) $ in Thousands		Jun. 30, 2016		Dec. 31, 2015
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		$ 1,496,821		$ 1,627,121
Current
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		1,413,659		1,624,710
30 to 59 days
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		6,200
60 to 89 days
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total	[1]	74,800
90 days or more
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		1,162		1,163
In foreclosure or bankruptcy proceedings
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		1,000	[2]	1,248	[3]
Non-Accrual
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		35,702	[4]	35,937	[5]
Commercial mortgage loans
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		1,315,301		1,427,328
Commercial mortgage loans | Current
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		1,309,101		1,427,328
Commercial mortgage loans | 30 to 59 days
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		6,200
Commercial mortgage loans | 60 to 89 days
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total	[1]	74,800
Commercial mortgage loans | Non-Accrual
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		17,235	[4]	15,645	[5]
Mezzanine Loans
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		142,582		169,556
Mezzanine Loans | Current
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		65,620		167,145
Mezzanine Loans | 90 days or more
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		1,162		1,163
Mezzanine Loans | In foreclosure or bankruptcy proceedings
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		1,000	[2]	1,248	[3]
Mezzanine Loans | Non-Accrual
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		10,553	[4]	12,346	[5]
Preferred Equity Interests
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		38,938		30,237
Preferred Equity Interests | Current
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		38,938		30,237
Preferred Equity Interests | Non-Accrual
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total		$ 7,914	[4]	$ 7,946	[5]

[1] Subsequent to June 30, 2016, this $74,800 loan became 90 days delinquent and was placed on non-accrual status.

[2] This loan was on non-accrual due to uncertainty over whether we will fully collect principal and interest.

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

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

[5] 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.