Securitizations and Variable Interest Entities - Schedule of Cost and Fair Value of Securities (Details) - Variable Interest Entity, Not Primary Beneficiary, Aggregated Disclosure $ in Thousands	Mar. 31, 2019 USD ($)
Variable Interest Entity [Line Items]
Amortized Cost	$ 19,531
Fair Value	19,531
Rated notes
Variable Interest Entity [Line Items]
Amortized Cost	16,940
Fair Value	16,940
Certificates and other assets
Variable Interest Entity [Line Items]
Amortized Cost	2,591
Fair Value	$ 2,591