Securities - Maturity of Debt Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Held for Investment, Contractual maturity of debt securities, Amortized Cost
Amortized cost, Within one year	$ 351	$ 350
Amortized cost, After one year but within five years	778	840
Amortized Cost	1,129	1,190
Available for sale, Contractual maturity of debt securities, Amortized Cost
Amortized Cost, Within one year	389,115	348,318
Amortized Cost, After one year but within five years	1,167,880	1,223,529
Amortized Cost, After five years but within ten years	10,278	10,331
Amortized Cost, After ten years	34,796	37,242
Amortized Cost	1,602,069	1,619,420
Held for Investment, Contractual maturity of debt securities, Estimated Fair Value
Estimated Fair Value, Within one year	351	350
Estimated Fair Value, After one year but within five years	778	840
Estimated Fair Value	1,129	1,190
Available for sale, Contractual maturity of debt securities, Estimated Fair Value
Estimated Fair Value, Within one year	382,870	341,645
Estimated Fair Value, After one year but within five years	1,108,898	1,167,973
Estimated Fair Value, After five years but within ten years	8,848	8,851
Estimated Fair Value, After ten years	32,906	35,436
Total debt securities	$ 1,533,522	$ 1,553,905