Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Thousands			1 Months Ended	3 Months Ended	6 Months Ended
	May 08, 2019	Sep. 20, 2017	May 31, 2019	Jun. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Commitment And Contingencies [Line Items]
Settlement agreement, amount to be paid by related securitization trust	$ 9,000			$ 9,000	$ 9,000
Settlement payment received			$ 9,000
Outstanding funding commitment				$ 485,951	$ 485,951	$ 625,916
Remaining operating lease term					12 years 9 months 18 days
Operating lease extended term					5 years
Incremental borrowing rate					12.60%
Operating Lease, Liability, Statement of Financial Position [Extensible List]				us-gaap:OtherLiabilities	us-gaap:OtherLiabilities
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]				us-gaap:OtherAssets	us-gaap:OtherAssets
Operating lease liability				$ 2,983	$ 2,983
Operating lease asset				308	308
Impairment charge on operating lease assets				2,076
Impairment charges of other fixed assets				705
Other General and Administrative Expenses
Commitment And Contingencies [Line Items]
Operating lease costs				107	214
Variable lease costs				74	153
Lending Arrangements
Commitment And Contingencies [Line Items]
Outstanding funding commitment				0	0
Note B
Commitment And Contingencies [Line Items]
Payment to purchase mortgage loan		$ 18,500
Mortgage loan principal to be received				$ 18,500	$ 18,500
Note A
Commitment And Contingencies [Line Items]
Payment to purchase mortgage loan		$ 190,000