Investments - Fair Value and Amortized Cost of Debt Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Investments, Debt and Equity Securities [Abstract]
Available-for-Sale, Amortized Cost, Within one year	$ 99,620
Available-for-Sale, Amortized Cost, One to five years	61,425
Available-for-Sale, Amortized Cost, Five to ten years	130,282
Available-for-Sale, Amortized Cost, After ten years	41,108
Available-for-Sale, Amortized Cost, Mortgage-backed securities	794,371
Available-for-Sale, Amortized Cost	1,126,806	$ 997,196
Available-for-Sale, Fair Value, Within one year	98,934
Available-for-Sale, Fair Value, One to five years	60,672
Available-for-Sale, Fair Value, Five to ten years	115,146
Available-for-Sale, Fair Value, After ten years	34,512
Available-for-Sale, Fair Value, Mortgage-backed securities	732,912
Available-for-Sale, Fair Value, Total debt securities	1,042,176	919,648
Held-to-Maturity, Amortized Cost, After ten years	1,114
Held-to-Maturity, Amortized Cost, Mortgage-backed securities	4,112
Held-to-Maturity, Amortized Cost	5,226	2,209
Held-to-Maturity, Fair Value, After ten years	1,144
Held-to-Maturity, Fair Value, Mortgage-backed securities	4,123
Held-to-Maturity, Fair Value, Total debt securities	$ 5,267	$ 2,250