Fair Value of Financial Instruments - Quantitative Information About Level 3 Fair Value Measurements (Detail) - Level 3 $ in Thousands	Dec. 31, 2019 USD ($) year	Dec. 31, 2018 USD ($) year
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
GSE CRT Embedded Derivatives | $	$ 10,281	$ 22,771
Measurement Input, Expected Term | Minimum
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
GSE CRT Embedded Derivatives, weighted average life	1.1	2.9
Measurement Input, Expected Term | Maximum
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
GSE CRT Embedded Derivatives, weighted average life	4.2	5.9
Measurement Input, Expected Term | Weighted Average
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
GSE CRT Embedded Derivatives, weighted average life | year	2.9	4.3