Asset-Backed Securities Issued - Summary of Carrying Value Components of Collateral for Asset-Backed Securities Issued and Outstanding (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral for ABS Issued	$ 1,259,774	$ 798,317
Residential loans
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral for ABS Issued	1,252,879	791,636
Restricted cash
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral for ABS Issued	151	148
Accrued interest receivable
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral for ABS Issued	3,391	1,000
REO
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral for ABS Issued	3,353	5,533
Legacy Sequoia
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral for ABS Issued	637,184	798,317
Legacy Sequoia | Residential loans
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral for ABS Issued	632,817	791,636
Legacy Sequoia | Restricted cash
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral for ABS Issued	147	148
Legacy Sequoia | Accrued interest receivable
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral for ABS Issued	867	1,000
Legacy Sequoia | REO
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral for ABS Issued	3,353	5,533
Sequoia Choice
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral for ABS Issued	622,590	0
Sequoia Choice | Residential loans
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral for ABS Issued	620,062	0
Sequoia Choice | Restricted cash
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral for ABS Issued	4	0
Sequoia Choice | Accrued interest receivable
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral for ABS Issued	2,524	0
Sequoia Choice | REO
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral for ABS Issued	$ 0	$ 0