Investments - Fair Value and Amortized Cost of Debt Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Investments, Debt and Equity Securities [Abstract]
Available-for-Sale, Amortized Cost, Within one year	$ 5,017
Available-for-Sale, Amortized Cost, One to five years	329,832
Available-for-Sale, Amortized Cost, Five to ten years	150,446
Available-for-Sale, Amortized Cost, After ten years	50,016
Available-for-Sale, Amortized Cost, Mortgage-backed securities	705,464
Available-for-Sale, Amortized Cost	1,240,775	$ 1,332,419
Available-for-Sale, Fair Value, Within one year	4,994
Available-for-Sale, Fair Value, One to five years	299,780
Available-for-Sale, Fair Value, Five to ten years	129,651
Available-for-Sale, Fair Value, After ten years	42,276
Available-for-Sale, Fair Value, Mortgage-backed securities	618,047
Available-for-Sale, Fair Value, Total debt securities	1,094,748	1,184,390
Held-to-Maturity, Amortized Cost, After ten years	1,115
Held-to-Maturity, Amortized Cost, Mortgage-backed securities	1,101
Held-to-Maturity, Amortized Cost	2,216	1,948
Held-to-Maturity, Fair Value, After ten years	1,142
Held-to-Maturity, Fair Value, Mortgage-backed securities	1,094
Held-to-Maturity, Fair Value, Total debt securities	$ 2,236	$ 1,973