Investment Securities - Maturity of Securities Available for Sale (Detail) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Net Investment Income [Line Items]
Due within one year, Amortized Cost	$ 6,253
Due within one year, Estimated Fair Value	6,179
Due after one but within five years, Amortized Cost	2,386
Due after one but within five years, Estimated Fair Value	2,233
Due after five but within ten years, Amortized Cost	32,009
Due after five but within ten years, Estimated Fair Value	27,116
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	40,648
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Fair Value	35,528
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Amortized Cost	837,261
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value	702,581
Amortized Cost	877,909	$ 898,702
Securities available for sale, at fair value	738,109	$ 762,661
Debt Securities [Member]
Net Investment Income [Line Items]
Amortized Cost	877,909
Securities available for sale, at fair value	738,109
US Government Agencies Debt Securities [Member]
Net Investment Income [Line Items]
Amortized Cost	341,000
Securities available for sale, at fair value	283,400
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Net Investment Income [Line Items]
Amortized Cost	496,200
Securities available for sale, at fair value	$ 419,200