Secured Debt Agreements, Net - Summary of Statistics for Asset-Specific Financings (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) SecurityLoan	Dec. 31, 2015 USD ($) SecurityLoan
Participating Mortgage Loans [Line Items]
Collateral assets, Book Value	$ 869,417
Financing provided, Book Value	676,333
Collateral assets, Principal Balance	876,083
Financing provided, Principal Balance	$ 679,207
Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Collateral assets, Book Value		$ 627,839
Collateral assets, Principal Balance		$ 631,524
Count | SecurityLoan	7	5
LIBOR [Member] | Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	4.84%	4.44%
JP Morgan [Member] | Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Term	2020-01	2020-01
Collateral assets, Book Value	$ 282,818	$ 272,632
Collateral assets, Principal Balance	$ 284,012	$ 274,878
Count | SecurityLoan	1	1
JP Morgan [Member] | LIBOR [Member] | Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	3.88%	3.88%
Citibank [Member] | Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Term	2020-11	2018-10
Collateral assets, Book Value	$ 203,555	$ 36,514
Collateral assets, Principal Balance	$ 203,656	$ 36,749
Count | SecurityLoan	2	1
Citibank [Member] | LIBOR [Member] | Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	4.40%	4.42%
Deutsche Bank [Member] | Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Term	2021-08
Collateral assets, Book Value	$ 180,866
Collateral assets, Principal Balance	$ 183,300
Count | SecurityLoan	1
Deutsche Bank [Member] | LIBOR [Member] | Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	5.18%
Bank of the Ozarks [Member] | Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Term	2020-04
Collateral assets, Book Value	$ 140,524
Collateral assets, Principal Balance	$ 143,164
Count | SecurityLoan	2
Bank of the Ozarks [Member] | LIBOR [Member] | Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	6.42%
Wells Fargo [Member] | Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Term	2019-12	2019-06
Collateral assets, Book Value	$ 61,654	$ 318,693
Collateral assets, Principal Balance	$ 61,951	$ 319,897
Count | SecurityLoan	1	3
Wells Fargo [Member] | LIBOR [Member] | Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	6.05%	4.92%
Asset-Specific Financings [Member]
Participating Mortgage Loans [Line Items]
Guarantee	$ 231,585	$ 102,579
Financing provided, Book Value		473,799
Financing provided, Principal Balance	$ 679,207	$ 474,655
Count | SecurityLoan	7	5
Asset-Specific Financings [Member] | LIBOR [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	2.60%	2.16%
Asset-Specific Financings [Member] | JP Morgan [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Term	2020-01	2020-01
Guarantee	$ 116,839	$ 53,623
Financing provided, Book Value	233,626	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	$ 39,663	$ 6,329
Financing provided, Book Value	158,609	25,293
Financing provided, Principal Balance	$ 158,652	$ 25,314
Count | SecurityLoan	2	1
Asset-Specific Financings [Member] | Citibank [Member] | LIBOR [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	2.42%	2.08%
Asset-Specific Financings [Member] | Deutsche Bank [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Term	2021-08
Guarantee	$ 66,410
Financing provided, Book Value	133,621
Financing provided, Principal Balance	$ 135,075
Count | SecurityLoan	1
Asset-Specific Financings [Member] | Deutsche Bank [Member] | LIBOR [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	3.03%
Asset-Specific Financings [Member] | Bank of the Ozarks [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Term	2020-04
Financing provided, Book Value	$ 107,323
Financing provided, Principal Balance	$ 108,435
Count | SecurityLoan	2
Asset-Specific Financings [Member] | Bank of the Ozarks [Member] | LIBOR [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	3.68%
Asset-Specific Financings [Member] | Wells Fargo [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Term	2019-12	2019-06
Guarantee	$ 8,673	$ 42,627
Financing provided, Book Value	43,154	234,115
Financing provided, Principal Balance	$ 43,366	$ 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	2.97%	2.37%