Investment Securities - Schedule of Amortized Cost and Estimated Fair Value of Investments Available-for-Sale by Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
AFS Amortized Cost [Abstract]
Amortized Cost	$ 1,700,233	$ 1,803,898
AFS Estimated Fair Value [Abstract]
Allowance for credit losses	(17)	(17)
Estimated Fair Value	1,474,945	1,598,666
HTM Amortized Cost [Abstract]
Allowance for credit losses	2,010	766
Total held-to-maturity securities, net of ACL	1,032,485	1,093,374
HTM Estimated Fair Value [Abstract]
Investment securities held-to-maturity	872,710	968,707
Debt Securities, Available-for-Sale and Held-to-Maturity [Abstract]
Amortized Cost	2,732,718	2,897,272
Estimated Fair Value	2,347,655	2,567,373
U.S. Treasury bonds (after one year through five years)
AFS Amortized Cost [Abstract]
U.S. Treasury bonds (after one year through five years)	49,868	49,793
AFS Estimated Fair Value [Abstract]
U.S. Treasury bonds (after one year through five years)	47,050	46,327
U. S. agency securities
AFS Amortized Cost [Abstract]
One year or less	544,988	549,137
After one year through five years	135,014	111,742
After five years through ten years	43,971	73,886
After ten years	12,105	13,012
Amortized Cost	736,078	747,777
AFS Estimated Fair Value [Abstract]
One year or less	485,494	490,699
After one year through five years	122,355	100,297
After five years through ten years	39,077	68,180
After ten years	9,351	10,552
Allowance for credit losses	0	0
Residential mortgage-backed securities
AFS Amortized Cost [Abstract]
U.S. Treasury bonds (after one year through five years)	848,555	937,557
Amortized Cost	848,555	937,557
AFS Estimated Fair Value [Abstract]
U.S. Treasury bonds (after one year through five years)	714,148	820,503
Allowance for credit losses	0	0
HTM Amortized Cost [Abstract]
One year or less	685,648	741,057
HTM Estimated Fair Value [Abstract]
One year or less	576,058	652,667
Investment securities held-to-maturity	576,058	652,667
Commercial mortgage-backed securities
AFS Amortized Cost [Abstract]
U.S. Treasury bonds (after one year through five years)	54,904	56,071
Amortized Cost	54,904	56,071
AFS Estimated Fair Value [Abstract]
U.S. Treasury bonds (after one year through five years)	48,004	50,213
Allowance for credit losses	0	0
HTM Amortized Cost [Abstract]
One year or less	91,337	92,557
HTM Estimated Fair Value [Abstract]
One year or less	74,532	80,564
Investment securities held-to-maturity	74,532	80,564
Municipal bonds
AFS Amortized Cost [Abstract]
One year or less	0	300
After one year through five years	0	1,444
After five years through ten years	8,828	8,956
After ten years	0	0
Amortized Cost	8,828	10,700
AFS Estimated Fair Value [Abstract]
One year or less	0	300
After one year through five years	0	1,488
After five years through ten years	7,802	8,299
After ten years	0	0
Allowance for credit losses	0	0
HTM Amortized Cost [Abstract]
One year or less	6,028	3,139
After one year through five years	35,000	35,579
After five years through ten years	72,011	77,262
After ten years	12,185	12,293
HTM Estimated Fair Value [Abstract]
One year or less	5,866	3,110
After one year through five years	31,813	33,743
After five years through ten years	60,765	67,945
After ten years	10,075	11,383
Investment securities held-to-maturity	108,519	116,181
Corporate bonds
AFS Amortized Cost [Abstract]
One year or less	0	0
After one year through five years	2,000	2,000
After five years through ten years	0	0
Amortized Cost	2,000	2,000
AFS Estimated Fair Value [Abstract]
One year or less	0	0
After one year through five years	1,681	1,825
After five years through ten years	0	0
Allowance for credit losses	(17)	(17)
HTM Amortized Cost [Abstract]
One year or less	27,011	23,954
After one year through five years	88,443	84,953
After five years through ten years	16,832	23,346
HTM Estimated Fair Value [Abstract]
One year or less	23,577	20,771
After one year through five years	76,666	77,997
After five years through ten years	13,358	20,527
Investment securities held-to-maturity	$ 113,601	$ 119,295