Investment Securities - Maturity of Securities Available for Sale (Detail) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Net Investment Income [Line Items]
Due within one year, Amortized Cost	$ 4,999
Due within one year, Estimated Fair Value	4,985
Due after one but within five years, Amortized Cost	8,880
Due after one but within five years, Estimated Fair Value	8,611
Due after five but within ten years, Amortized Cost	28,645
Due after five but within ten years, Estimated Fair Value	24,764
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	42,524
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Fair Value	38,360
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Amortized Cost	884,351
Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value	749,055
Amortized Cost	926,875	$ 1,045,579
Securities available for sale, at fair value	787,415	$ 1,041,380
Debt Securities [Member]
Net Investment Income [Line Items]
Amortized Cost	926,875
Securities available for sale, at fair value	787,415
US Government Agencies Debt Securities [Member]
Net Investment Income [Line Items]
Amortized Cost	339,200
Securities available for sale, at fair value	287,500
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Net Investment Income [Line Items]
Amortized Cost	545,200
Securities available for sale, at fair value	$ 461,500