Commercial Real Estate Investments - Additional Information (Detail) (USD $)	1 Months Ended		3 Months Ended			1 Months Ended
	Nov. 30, 2014 Property	Jan. 31, 2014	Mar. 31, 2015		Mar. 31, 2014	Feb. 28, 2015	Dec. 31, 2014
Real Estate Properties [Line Items]
Percentage of ownership interest in joint venture	90.00%
Number of retail property Acquired	11
Principal amount of mortgage loan			$ 146,361,000				$ 146,430,000
Weighted average amortization period for intangible assets and liabilities			3 years 8 months 12 days
Percentage of non-controlling interest			10.00%
Fair value of non-controlling interest at acquisition date			15,400,000
Depreciation expense			2,823,000		292,000
Securitization financing transaction, purchase		399,500,000
Securitization financing transaction, total		260,700,000	1,491,829,000	[1]			260,700,000	[1],[2]
Securitization financing transaction, weighted average rate		65.30%
Securitization financing transaction, variable interest rate		1.74%
Securitization financing transaction, variable interest rate description			LIBOR plus 1.74% at closing
Senior Secured mortgages of Consolidated VIE			361,200,000				398,600,000	[2]
Unamortized origination fees			700,000
General and Administrative Expense [Member]
Real Estate Properties [Line Items]
Transaction costs related to acquisitions			0
Depreciation expense			2,800,000		300,000
FREMF Trust
Real Estate Properties [Line Items]
Transaction costs related to acquisitions			(810,000)
Exposure to the obligations of the VIE limited to the amount of investment						102,100,000
Gain (Loss) recognized upon initial consolidation						0
Debt issue costs expensed						600,000
Variable interest entity, consolidated, carrying amount, assets			1,400,000
Variable interest entity, consolidated, carrying amount, liabilities			1,300,000
Mortgage loans held and securitized debt obligations, unpaid principal balance			1,400,000,000
Loans 90 days or more past due or on nonaccrual status			0
Gain (Loss) attributable to instrument- specific credit risk			0
Freddie Mac | Floating Rate Multifamily Mortgage Loans
Real Estate Properties [Line Items]
Number of loans in the underlying portfolio						11
Principal balance						1,400,000,000
Ten Year Four Point Zero Three Percent Fixed Rate Interest Only Mortgage Loan[Member]
Real Estate Properties [Line Items]
Principal amount of mortgage loan	104,000,000
Debt term	10 years
Debt instrument, interest rate	4.03%
Other Assets
Real Estate Properties [Line Items]
Securitization cost		$ 4,300,000

[1] Includes securitized debt of a consolidated VIE carried at fair value of $1.3 billion and $0 at March 31, 2015 and December 31, 2014, respectively.

[2] Derived from the audited consolidated financial statements at December 31, 2014.