Investment Securities - Maturity of Securities Available for Sale (Detail) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Net Investment Income [Line Items]
Due within one year, Amortized Cost	$ 4,998
Due within one year, Estimated Fair Value	5,007
Due after one but within five years, Amortized Cost	8,879
Due after one but within five years, Estimated Fair Value	8,808
Due after five but within ten years, Amortized Cost	28,669
Due after five but within ten years, Estimated Fair Value	26,713
Due after ten years, Amortized Cost	0
Due after ten years, Estimated Fair Value	0
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Amortized Cost	42,546
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Fair Value	40,528
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Amortized Cost	914,324
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value	823,094
Amortized Cost	956,870	$ 1,045,579
Securities available for sale, at fair value	863,622	$ 1,041,380
Debt Securities [Member]
Net Investment Income [Line Items]
Amortized Cost	956,870
Securities available for sale, at fair value	863,622
US Government Agencies Debt Securities [Member]
Net Investment Income [Line Items]
Amortized Cost	347,400
Securities available for sale, at fair value	313,600
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Net Investment Income [Line Items]
Amortized Cost	566,900
Securities available for sale, at fair value	$ 509,500