Commercial Real Estate Investments - Additional Information (Detail)		1 Months Ended					3 Months Ended			12 Months Ended
	Dec. 11, 2015 USD ($)	Apr. 30, 2016 USD ($)	Feb. 29, 2016 USD ($) Loan	Apr. 30, 2015 USD ($) Loan	Feb. 28, 2015 USD ($) Loan	Jan. 31, 2014 USD ($)	Mar. 31, 2016 USD ($)		Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)
Real Estate Properties [Line Items]
Sales of senior loan										$ 46,945,000
Weighted average amortization period for intangible assets and liabilities							7 years 2 months 12 days
Depreciation expense							$ 4,570,000		$ 2,823,000
Securitization financing transaction, purchase						$ 399,500,000
Securitization financing transaction, total						$ 260,700,000	3,802,682,000	[1]		2,540,711,000	[1],[2]
Securitization financing transaction, weighted average rate						65.30%
Securitization cost						$ 4,300,000
Carrying value of trust's liabilities							125,600,000
Senior Secured mortgages of Consolidated VIE							211,900,000			262,700,000	[2]
Unamortized origination fees							200,000
Deferred financing costs							200,000
FREMF Trust
Real Estate Properties [Line Items]
Exposure to the obligations of the VIE limited to the amount of investment					$ 291,000,000
Gain (Loss) recognized upon initial consolidation					0
Debt issue costs expensed							200,000		800,000
Mortgage loans, unpaid principal balance							4,000,000,000
Loans 90 days or more past due or on nonaccrual status							0
Gain (Loss) attributable to instrument- specific credit risk							0
Freddie Mac | FREMF 2015-KLSF [Member] | FREMF Trust
Real Estate Properties [Line Items]
Variable interest entity, consolidated, carrying amount, assets							1,300,000,000
Variable interest entity, consolidated, carrying amount, liabilities							1,200,000,000
Payment to purchase mortgage loans					$ 102,100,000
Freddie Mac | FREMF 2015-KF07 | FREMF Trust
Real Estate Properties [Line Items]
Variable interest entity, consolidated, carrying amount, assets							1,100,000,000
Variable interest entity, consolidated, carrying amount, liabilities							1,000,000,000
Payment to purchase mortgage loans				$ 89,400,000
Freddie Mac | FREM 2016-KLH1 [Member] | FREMF Trust
Real Estate Properties [Line Items]
Face value			$ 107,600,000
Variable interest entity, consolidated, carrying amount, assets							1,500,000,000
Variable interest entity, consolidated, carrying amount, liabilities							$ 1,400,000,000
Payment to purchase mortgage loans			107,600,000
Discounted value			$ 4,400,000
Freddie Mac | Floating Rate Multifamily Mortgage Loans [Member] | FREMF 2015-KLSF [Member]
Real Estate Properties [Line Items]
Number of loans in the underlying portfolio | Loan					11
Face value					$ 1,400,000,000
Freddie Mac | Floating Rate Multifamily Mortgage Loans [Member] | FREMF 2015-KF07
Real Estate Properties [Line Items]
Number of loans in the underlying portfolio | Loan				40
Face value				$ 1,200,000,000
Freddie Mac | Floating Rate Multifamily Mortgage Loans [Member] | FREM 2016-KLH1 [Member]
Real Estate Properties [Line Items]
Number of loans in the underlying portfolio | Loan			28
Face value			$ 1,500,000,000
Commercial Mortgage Trust Mo One [Member]
Real Estate Properties [Line Items]
Securitization financing transaction, variable interest rate						1.74%
Securitization financing transaction, variable interest rate description							LIBOR plus 1.74% at closing
Commercial Mortgage Loan [Member]
Real Estate Properties [Line Items]
Debt issued							$ 338,346,000			$ 338,444,000
CALIFORNIA | Commercial Mortgage Loan [Member] | Eight Class AB Office Properties In Orange Country California [Member]
Real Estate Properties [Line Items]
Funding for senior mortgage loan, net of origination fees	$ 278,600,000
Future funding commitment	30,000,000
Funding for senior mortgage loan, net of origination fees	280,000,000
Debt issued	335,000,000
CALIFORNIA | Commercial Mortgage Loan [Member] | Eight Class AB Office Properties In Orange Country California [Member] | Subsequent Event
Real Estate Properties [Line Items]
Sales of senior loan		$ 115,000,000
Gain on sales of senior loan		0
CALIFORNIA | Commercial Mortgage Loan [Member] | Eight Class AB Office Properties In Orange Country California [Member] | Mezzanine Loans
Real Estate Properties [Line Items]
Funding for senior mortgage loan, net of origination fees	52,700,000
Debt issued	$ 55,000,000
CALIFORNIA | Commercial Mortgage Loan [Member] | Senior Loans | Eight Class AB Office Properties In Orange Country California [Member] | Subsequent Event
Real Estate Properties [Line Items]
Remains senior loan held for sale		$ 165,000,000
Other Operating Income (Expense) [Member]
Real Estate Properties [Line Items]
Depreciation expense							$ 4,600,000		$ 2,800,000

[1] Includes securitized debt of consolidated VIEs carried at fair value of $3.7 billion and $2.4 billion at March 31, 2016 and December 31, 2015, respectively.

[2] Derived from the audited consolidated financial statements at December 31, 2015.