Investments - Schedule of Amortized Cost and Fair Value on Mortgage-Backed and Asset-Backed Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,150,524	$ 1,061,192
Fair Value	996,783	1,040,455
Mortgage-backed and asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	332,444	322,844
Fair Value	289,733	316,118
Agency \| Mortgage-backed securities:
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	159,177	147,992
Fair Value	133,795	143,819
Non-agency \| Mortgage-backed securities:
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	61,880	59,906
Fair Value	51,242	58,263
Auto loan receivables \| Asset-backed securities:
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	66,392	67,352
Fair Value	63,258	66,877
Credit card receivables \| Asset-backed securities:
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	657	4,741
Fair Value	611	4,719
Other receivables \| Asset-backed securities:
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	44,338	42,853
Fair Value	$ 40,827	$ 42,440