Secured Debt Agreements, Net - Summary of Statistics for Asset-Specific Financings (Detail) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017 USD ($) SecurityLoan	Dec. 31, 2016 USD ($) SecurityLoan
Participating Mortgage Loans [Line Items]
Collateral assets, Book Value	$ 720,315	$ 869,417
Financing provided, Book Value	566,190	676,333
Collateral assets, Principal Balance	724,013	876,083
Financing provided, Principal Balance	$ 567,577	$ 679,207
Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Count | SecurityLoan	6	7
LIBOR [Member] | Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	4.83%	4.84%
JP Morgan [Member] | Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Term	2020-01	2020-01
Collateral assets, Book Value	$ 285,955	$ 282,818
Collateral assets, Principal Balance	$ 286,887	$ 284,012
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	2020-11
Collateral assets, Book Value	$ 204,548	$ 203,555
Collateral assets, Principal Balance	$ 204,617	$ 203,656
Count | SecurityLoan	2	2
Citibank [Member] | LIBOR [Member] | Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	4.40%	4.40%
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	2020-06	2020-04
Collateral assets, Book Value	$ 167,510	$ 140,524
Collateral assets, Principal Balance	$ 169,986	$ 143,164
Count | SecurityLoan	2	2
Bank of the Ozarks [Member] | LIBOR [Member] | Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	6.51%	6.42%
Wells Fargo [Member] | Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Term	2019-12	2019-12
Collateral assets, Book Value	$ 62,302	$ 61,654
Collateral assets, Principal Balance	$ 62,523	$ 61,951
Count | SecurityLoan	1	1
Wells Fargo [Member] | LIBOR [Member] | Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	6.05%	6.05%
Asset-Specific Financings [Member]
Participating Mortgage Loans [Line Items]
Guarantee	$ 165,883	$ 231,585
Financing provided, Principal Balance	$ 567,577	$ 679,207
Count | SecurityLoan	6	7
Asset-Specific Financings [Member] | LIBOR [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	2.58%	2.60%
Asset-Specific Financings [Member] | JP Morgan [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Term	2020-01	2020-01
Guarantee	$ 116,839	$ 116,839
Financing provided, Book Value	233,413	233,626
Financing provided, Principal Balance	$ 233,679	$ 233,679
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%	1.89%
Asset-Specific Financings [Member] | Citibank [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Term	2020-11	2020-11
Guarantee	$ 40,291	$ 39,663
Financing provided, Book Value	161,123	158,609
Financing provided, Principal Balance	$ 161,163	$ 158,652
Count | SecurityLoan	2	2
Asset-Specific Financings [Member] | Citibank [Member] | LIBOR [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	2.42%	2.42%
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	2020-06	2020-04
Financing provided, Book Value	$ 128,045	$ 107,323
Financing provided, Principal Balance	$ 128,969	$ 108,435
Count | SecurityLoan	2	2
Asset-Specific Financings [Member] | Bank of the Ozarks [Member] | LIBOR [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	3.83%	3.68%
Asset-Specific Financings [Member] | Wells Fargo [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Term	2019-12	2019-12
Guarantee	$ 8,753	$ 8,673
Financing provided, Book Value	43,609	43,154
Financing provided, Principal Balance	$ 43,766	$ 43,366
Count | SecurityLoan	1	1
Asset-Specific Financings [Member] | Wells Fargo [Member] | LIBOR [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	3.14%	2.97%