Delinquency Statistics of Commercial Real Estate Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2019		Dec. 31, 2018
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total	$ 438,542		$ 502,974
Commercial Mortgage Loans
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total	388,913		453,283
Mezzanine Loans
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total	21,114		21,114
Preferred Equity Interests
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total	28,515		28,577
Current
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total	401,535		455,534
Current | Commercial Mortgage Loans
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total	351,906		414,735
Current | Mezzanine Loans
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total	21,114		12,222
Current | Preferred Equity Interests
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total	28,515		28,577
90 days or more
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total	37,007		47,440
90 days or more | Commercial Mortgage Loans
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total	37,007		47,440
Non-accrual
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total	81,967	[1]	92,993	[2]
Non-accrual | Commercial Mortgage Loans
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total	65,952	[1]	46,793	[2]
Non-accrual | Mezzanine Loans
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total	8,245	[1]	8,892	[2]
Non-accrual | Preferred Equity Interests
Mortgage Loans On Real Estate [Line Items]
Delinquency statistics, Total	$ 7,770	[1]	$ 37,308	[2]

[1] Includes five loans that are current but are on non-accrual status due to uncertainty over whether we will fully collect principal and interest. Also includes two loans that are 90 days or more past due in accordance with their terms.

[2] Includes five loans that are current but are on non-accrual status due to uncertainty over whether we will fully collect principal and interest. Also includes three loans that are 90 days or more past due in accordance with their terms.