Securitized Debt Obligations, Net - Schedule of Information on Securitized Debt Obligations (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) Loans	Jun. 30, 2017 USD ($)
Debt Instrument [Line Items]
Principal Balance		$ 474,600
Financing Provided [Member]
Debt Instrument [Line Items]
Count | Loans	2
Principal Balance	$ 1,292,120
Book Value	$ 1,282,411
Financing Provided [Member] | Collateralized Loan Obligations [Member]
Debt Instrument [Line Items]
Count | Loans	1
Principal Balance	$ 817,500
Book Value	$ 808,083
Term	2035-06
Financing Provided [Member] | Single Asset Securitization [Member]
Debt Instrument [Line Items]
Count | Loans	1
Principal Balance	$ 474,620
Book Value	$ 474,328
Term	2033-06
Collateral Assets [Member]
Debt Instrument [Line Items]
Count | Loans	32
Principal Balance	$ 1,656,406
Book Value	$ 1,652,880
Collateral Assets [Member] | Collateralized Loan Obligations [Member]
Debt Instrument [Line Items]
Count | Loans	31
Principal Balance	$ 1,000,000
Book Value	$ 1,000,000
Term	2021-10
Collateral Assets [Member] | Single Asset Securitization [Member]
Debt Instrument [Line Items]
Count | Loans	1
Principal Balance	$ 656,406
Book Value	$ 652,880
Term	2023-06
LIBOR [Member] | Financing Provided [Member]
Debt Instrument [Line Items]
Wtd.Avg.Yield/Cost	1.83%
LIBOR [Member] | Financing Provided [Member] | Collateralized Loan Obligations [Member]
Debt Instrument [Line Items]
Wtd.Avg.Yield/Cost	1.76%
LIBOR [Member] | Financing Provided [Member] | Single Asset Securitization [Member]
Debt Instrument [Line Items]
Wtd.Avg.Yield/Cost	1.94%
LIBOR [Member] | Collateral Assets [Member]
Debt Instrument [Line Items]
Wtd.Avg.Yield/Cost	5.17%
LIBOR [Member] | Collateral Assets [Member] | Collateralized Loan Obligations [Member]
Debt Instrument [Line Items]
Wtd.Avg.Yield/Cost	5.16%
LIBOR [Member] | Collateral Assets [Member] | Single Asset Securitization [Member]
Debt Instrument [Line Items]
Wtd.Avg.Yield/Cost	3.60%