Secured Debt Agreements - Summary of Statistics for Asset-Specific Financings (Detail) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2016 USD ($) SecurityLoan	Dec. 31, 2015 USD ($) SecurityLoan
Participating Mortgage Loans [Line Items]
Collateral assets, Book Value	$ 614,532
Financing provided, Book Value	488,634
Collateral assets, Principal Balance	619,811
Financing provided, Principal Balance	$ 490,702
Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Collateral assets, Book Value		$ 627,839
Collateral assets, Principal Balance		$ 631,524
Count | SecurityLoan	6	5
LIBOR [Member] | Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	4.57%	4.44%
JP Morgan [Member] | Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Term	2020-01	2020-01
Collateral assets, Book Value	$ 278,709	$ 272,632
Collateral assets, Principal Balance	$ 280,415	$ 274,878
Count | SecurityLoan	1	1
JP Morgan [Member] | LIBOR [Member] | Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	3.87%	3.88%
Citibank [Member] | Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Term	2020-11	2018-10
Collateral assets, Book Value	$ 201,101	$ 36,514
Collateral assets, Principal Balance	$ 201,270	$ 36,749
Count | SecurityLoan	2	1
Citibank [Member] | LIBOR [Member] | Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	4.45%	4.42%
Bank of the Ozarks [Member] | Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Term	2019-11
Collateral assets, Book Value	$ 70,823
Collateral assets, Principal Balance	$ 73,751
Count | SecurityLoan	2
Bank of the Ozarks [Member] | LIBOR [Member] | Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	6.00%
Wells Fargo [Member] | Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Term	2019-12	2019-06
Collateral assets, Book Value	$ 63,899	$ 318,693
Collateral assets, Principal Balance	$ 64,375	$ 319,897
Count | SecurityLoan	1	3
Wells Fargo [Member] | LIBOR [Member] | Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	6.32%	4.92%
Asset-Specific Financings [Member]
Participating Mortgage Loans [Line Items]
Guarantee	$ 106,547	$ 102,579
Financing provided, Book Value		473,799
Financing provided, Principal Balance	$ 490,702	$ 474,655
Count | SecurityLoan	6	5
Asset-Specific Financings [Member] | LIBOR [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	2.41%	2.16%
Asset-Specific Financings [Member] | JP Morgan [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Term	2020-01	2020-01
Guarantee	$ 58,420	$ 53,623
Financing provided, Book Value	233,456	214,391
Financing provided, Principal Balance	$ 233,679	$ 214,491
Count | SecurityLoan	1	1
Asset-Specific Financings [Member] | JP Morgan [Member] | LIBOR [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	1.89%	1.94%
Asset-Specific Financings [Member] | Citibank [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Term	2020-11	2018-10
Guarantee	$ 39,115	$ 6,329
Financing provided, Book Value	156,446	25,293
Financing provided, Principal Balance	$ 156,461	$ 25,314
Count | SecurityLoan	2	1
Asset-Specific Financings [Member] | Citibank [Member] | LIBOR [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	2.45%	2.08%
Asset-Specific Financings [Member] | Bank of the Ozarks [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Term	2019-11
Financing provided, Book Value	$ 54,003
Financing provided, Principal Balance	$ 55,500
Count | SecurityLoan	2
Asset-Specific Financings [Member] | Bank of the Ozarks [Member] | LIBOR [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	3.84%
Asset-Specific Financings [Member] | Wells Fargo [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Term	2019-12	2019-06
Guarantee	$ 9,012	$ 42,627
Financing provided, Book Value	44,729	234,115
Financing provided, Principal Balance	$ 45,062	$ 234,850
Count | SecurityLoan	1	3
Asset-Specific Financings [Member] | Wells Fargo [Member] | LIBOR [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	3.20%	2.37%