Schedule IV - Mortgage Loans on Real Estate (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013
Mortgage Loans on Real Estate [Line Items]
Prior Liens	$ 398,235
Face Amount of Loans	2,221,678
Carrying Amount of Loans	2,087,888
Senior Mortgage Loans [Member]
Mortgage Loans on Real Estate [Line Items]
Prior Liens
Face Amount of Loans	1,811,513
Carrying Amount of Loans	1,800,329
Senior Mortgage Loans [Member] | Various / Diversified [Member] | All Other Mortgage Loans Individually Less Than 3% [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Various / Diversified
Debt instrument variable rate basis	LIBOR
Maximum Maturity Date	Jan. 09, 2019
Prior Liens
Face Amount of Loans	628,747
Carrying Amount of Loans	623,829
Maximum Maturity Date - earliest	Nov. 06, 2016
Senior Mortgage Loans [Member] | Office [Member] | Borrower A [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Office / West
Debt instrument variable rate basis	LIBOR
Interest Payment Rates	3.80%
Maximum Maturity Date	Jun. 15, 2018
Periodic Payment Terms	I/O
Prior Liens
Face Amount of Loans	193,980
Carrying Amount of Loans	193,194
Senior Mortgage Loans [Member] | Office [Member] | Borrower D [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Office / Northeast
Debt instrument variable rate basis	LIBOR
Interest Payment Rates	4.75%
Maximum Maturity Date	Jan. 09, 2019
Periodic Payment Terms	I/O
Prior Liens
Face Amount of Loans	140,000
Carrying Amount of Loans	138,627
Senior Mortgage Loans [Member] | Office [Member] | Borrower H [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Office / West
Debt instrument variable rate basis	LIBOR
Interest Payment Rates	3.95%
Maximum Maturity Date	Jun. 09, 2018
Periodic Payment Terms	I/O
Prior Liens
Face Amount of Loans	70,284
Carrying Amount of Loans	70,131
Senior Mortgage Loans [Member] | Office [Member] | Borrower I [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Office / Northeast
Debt instrument variable rate basis	LIBOR
Interest Payment Rates	4.00%
Maximum Maturity Date	Jun. 10, 2016
Periodic Payment Terms	I/O
Prior Liens
Face Amount of Loans	68,000
Carrying Amount of Loans	67,787
Senior Mortgage Loans [Member] | Diversified [Member] | Borrower C [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Diversified / Northeast
Debt instrument variable rate basis	LIBOR
Interest Payment Rates	3.70%
Maximum Maturity Date	Sep. 30, 2020
Periodic Payment Terms	I/O
Prior Liens
Face Amount of Loans	140,000
Carrying Amount of Loans	139,695
Senior Mortgage Loans [Member] | Diversified [Member] | Borrower F [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Diversified / Diversified
Debt instrument variable rate basis	LIBOR
Interest Payment Rates	4.25%
Maximum Maturity Date	Aug. 10, 2018
Periodic Payment Terms	I/O
Prior Liens
Face Amount of Loans	87,038
Carrying Amount of Loans	86,489
Senior Mortgage Loans [Member] | Multifamily [Member] | Borrower B [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Multifamily / Northeast
Debt instrument variable rate basis	LIBOR
Interest Payment Rates	4.50%
Maximum Maturity Date	Nov. 09, 2018
Periodic Payment Terms	I/O
Prior Liens
Face Amount of Loans	181,000
Carrying Amount of Loans	179,266
Senior Mortgage Loans [Member] | Multifamily [Member] | Borrower G [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Multifamily / Southeast
Debt instrument variable rate basis	LIBOR
Interest Payment Rates	3.85%
Maximum Maturity Date	Jul. 09, 2018
Periodic Payment Terms	I/O
Prior Liens
Face Amount of Loans	81,000
Carrying Amount of Loans	80,664
Senior Mortgage Loans [Member] | Hotel / West [Member] | Borrower E [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Hotel / West
Debt instrument variable rate basis	LIBOR
Interest Payment Rates	4.38%
Maximum Maturity Date	Nov. 09, 2018
Periodic Payment Terms	I/O
Prior Liens
Face Amount of Loans	89,750
Carrying Amount of Loans	89,161
Senior Mortgage Loans [Member] | Other [Member] | Borrower J [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Other / Diversified
Debt instrument variable rate basis	LIBOR
Interest Payment Rates	5.00%
Maximum Maturity Date	Sep. 14, 2018
Periodic Payment Terms	I/O
Prior Liens
Face Amount of Loans	67,714
Carrying Amount of Loans	66,956
Senior Mortgage Loans [Member] | Other [Member] | Borrower K [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Other / Northeast
Debt instrument variable rate basis	LIBOR
Interest Payment Rates	8.00%
Maximum Maturity Date	Feb. 09, 2015
Periodic Payment Terms	I/O
Prior Liens
Face Amount of Loans	64,000
Carrying Amount of Loans	64,530
Subordinate Loans [Member]
Mortgage Loans on Real Estate [Line Items]
Prior Liens	398,235
Face Amount of Loans	410,164
Carrying Amount of Loans	287,559
Subordinate Loans [Member] | Various / Diversified [Member] | All Other Floating-Rate Loans Individually Less Than 3% [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Various / Diversified
Debt instrument variable rate basis	LIBOR
Maximum Maturity Date	Dec. 09, 2014
Prior Liens
Face Amount of Loans	178,820
Carrying Amount of Loans	63,990
Maximum Maturity Date - earliest	Jan. 08, 2014
Subordinate Loans [Member] | Various / Diversified [Member] | All Other Fixed-Rate Loans Individually Less Than 3% [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Various / Diversified
Maximum Maturity Date	Feb. 01, 2016
Prior Liens
Face Amount of Loans	23,995
Carrying Amount of Loans	23,675
Maximum Maturity Date - earliest	Jun. 01, 2014
Subordinate Loans [Member] | Office [Member] | Borrower AA [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Office / Northwest
Debt instrument variable rate basis	LIBOR
Interest Payment Rates	5.66%
Maximum Maturity Date	Apr. 09, 2015
Periodic Payment Terms	I/O
Prior Liens	289,318
Face Amount of Loans	173,837
Carrying Amount of Loans	166,207
Subordinate Loans [Member] | Multifamily [Member] | Borrower BB [Member]
Mortgage Loans on Real Estate [Line Items]
Location	Multifamily / Northeast
Debt instrument variable rate basis	LIBOR
Interest Payment Rates	12.56%
Maximum Maturity Date	Dec. 13, 2017
Periodic Payment Terms	I/O
Prior Liens	108,917
Face Amount of Loans	33,513
Carrying Amount of Loans	$ 33,687
Minimum [Member] | Senior Mortgage Loans [Member] | Various / Diversified [Member] | All Other Mortgage Loans Individually Less Than 3% [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	3.85%
Minimum [Member] | Subordinate Loans [Member] | Various / Diversified [Member] | All Other Floating-Rate Loans Individually Less Than 3% [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	3.53%
Minimum [Member] | Subordinate Loans [Member] | Various / Diversified [Member] | All Other Fixed-Rate Loans Individually Less Than 3% [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	8.00%
Maximum [Member] | Senior Mortgage Loans [Member] | Various / Diversified [Member] | All Other Mortgage Loans Individually Less Than 3% [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	5.00%
Maximum [Member] | Subordinate Loans [Member] | Various / Diversified [Member] | All Other Floating-Rate Loans Individually Less Than 3% [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	6.06%
Maximum [Member] | Subordinate Loans [Member] | Various / Diversified [Member] | All Other Fixed-Rate Loans Individually Less Than 3% [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Payment Rates	8.77%