Securities - Maturity of Debt Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Held for Investment, Contractual maturity of debt securities, Amortized Cost
Amortized cost, Within one year	$ 350	$ 1,186
Amortized cost, After one year but within five years	841	1,195
Amortized cost, After five years but within ten years	1	2
Amortized Cost	1,192	2,383
Available for sale, Contractual maturity of debt securities, Amortized Cost
Amortized Cost, Within one year	208,397	101,607
Amortized Cost, After one year but within five years	1,317,661	1,316,874
Amortized Cost, After five years but within ten years	60,974	170,513
Amortized Cost, After ten years	38,273	42,897
Amortized Cost	1,625,305	1,631,891
Held for Investment, Contractual maturity of debt securities, Estimated Fair Value
Estimated Fair Value, Within one year	350	1,186
Estimated Fair Value, After one year but within five years	841	1,195
Estimated Fair Value, After five years but within ten years	1	2
Estimated Fair Value	1,192	2,383
Available for sale, Contractual maturity of debt securities, Estimated Fair Value
Estimated Fair Value, Within one year	203,774	100,655
Estimated Fair Value, After one year but within five years	1,228,720	1,233,725
Estimated Fair Value, After five years but within ten years	56,159	163,101
Estimated Fair Value, After ten years	35,603	40,740
Total debt securities	$ 1,524,256	$ 1,538,221