Securitized Debt - Callable Debt (Detail) - Securitized Loans $ in Thousands	Dec. 31, 2017 USD ($)
Debt Instrument, Redemption [Line Items]
2018	$ 943,573
2019	397,734
2020	4,744,768
2021	2,811,850
2022	287,157
Total	$ 9,185,082