Securities - Amortized Cost and Fair Value of Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Securities available-for-sale [Abstract]
Amortized Cost	$ 4,266,261	$ 3,871,491
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax	3,348	12,805
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax	405,912	325,426
Fair Value	3,863,697	3,558,870
Available-for-sale, Amortized Cost [Abstract]
Due in one year or less	20,932
Due in one year to five years	121,345
Due in five years to ten years	623,763
Due after ten years	2,270,077
Mortgage-backed securities	1,051,931
Asset-backed securities	178,213
Amortized Cost	4,266,261	3,871,491
Available-for-sale, Fair Value [Abstract]
Due in one year or less	22,591
Due in one year to five years	128,684
Due in five years to ten years	550,333
Due after ten years	2,110,720
Mortgage-backed securities	887,907
Asset-backed securities	163,462
Fair Value	3,863,697	3,558,870
Securities held-to-maturity [Abstract]
Amortized Cost	3,020,287	3,080,658
Gross Unrealized Gains	0	2,268
Gross Unrealized Losses	439,055	337,980
Fair Value	2,581,232	2,744,946
Allowance for credit losses - securities held-to-maturity	1,708	1,608
Debt Securities, Held-to-Maturity, Amortized Cost, after Allowance for Credit Loss	3,018,579	3,079,050
Held-to-maturity, Amortized Cost [Abstract]
Due in one year or less	19,901
Due in one year to five years	396,635
Due in five years to ten years	132,910
Due after ten years	1,886,096
Mortgage-backed securities	386,095
Asset-backed securities	198,650
Amortized Cost	3,020,287	3,080,658
Held-to-maturity, Fair Value [Abstract]
Due in one year or less	19,059
Due in one year to five years	367,156
Due in five years to ten years	117,293
Due after ten years	1,562,186
Mortgage-backed securities	335,533
Asset-backed securities	180,005
Fair Value	2,581,232	2,744,946
U.S. Treasury securities
Securities available-for-sale [Abstract]
Amortized Cost	732,128	196,151
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax	1	0
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax	2,973	1,967
Fair Value	729,156	194,184
Available-for-sale, Amortized Cost [Abstract]
Amortized Cost	732,128	196,151
Available-for-sale, Fair Value [Abstract]
Fair Value	729,156	194,184
Securities held-to-maturity [Abstract]
Amortized Cost	90,417	92,738
Gross Unrealized Gains	0	0
Gross Unrealized Losses	5,416	6,472
Fair Value	85,001	86,266
Held-to-maturity, Amortized Cost [Abstract]
Amortized Cost	90,417	92,738
Held-to-maturity, Fair Value [Abstract]
Fair Value	85,001	86,266
U.S. Government agency securities
Securities available-for-sale [Abstract]
Amortized Cost	284,739	432,475
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax	0	0
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax	29,634	36,318
Fair Value	255,105	396,157
Available-for-sale, Amortized Cost [Abstract]
Amortized Cost	284,739	432,475
Available-for-sale, Fair Value [Abstract]
Fair Value	255,105	396,157
Securities held-to-maturity [Abstract]
Amortized Cost	364,641	374,255
Gross Unrealized Gains	0	0
Gross Unrealized Losses	29,030	27,860
Fair Value	335,611	346,395
Held-to-maturity, Amortized Cost [Abstract]
Amortized Cost	364,641	374,255
Held-to-maturity, Fair Value [Abstract]
Fair Value	335,611	346,395
Mortgage-backed securities
Securities available-for-sale [Abstract]
Amortized Cost	1,051,931	1,114,948
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax	131	211
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax	164,155	143,583
Fair Value	887,907	971,576
Available-for-sale, Amortized Cost [Abstract]
Amortized Cost	1,051,931	1,114,948
Available-for-sale, Fair Value [Abstract]
Fair Value	887,907	971,576
Securities held-to-maturity [Abstract]
Amortized Cost	386,095	413,119
Gross Unrealized Gains	0	52
Gross Unrealized Losses	50,562	41,593
Fair Value	335,533	371,578
Held-to-maturity, Amortized Cost [Abstract]
Amortized Cost	386,095	413,119
Held-to-maturity, Fair Value [Abstract]
Fair Value	335,533	371,578
State and municipal securities
Securities available-for-sale [Abstract]
Amortized Cost	1,547,266	1,478,310
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax	3,142	12,553
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax	139,285	78,557
Fair Value	1,411,123	1,412,306
Available-for-sale, Amortized Cost [Abstract]
Amortized Cost	1,547,266	1,478,310
Available-for-sale, Fair Value [Abstract]
Fair Value	1,411,123	1,412,306
Securities held-to-maturity [Abstract]
Amortized Cost	1,893,923	1,927,778
Gross Unrealized Gains	0	2,216
Gross Unrealized Losses	324,216	233,564
Fair Value	1,569,707	1,696,430
Held-to-maturity, Amortized Cost [Abstract]
Amortized Cost	1,893,923	1,927,778
Held-to-maturity, Fair Value [Abstract]
Fair Value	1,569,707	1,696,430
Asset-backed securities
Securities available-for-sale [Abstract]
Amortized Cost	178,213	134,386
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax	2	0
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax	14,753	16,983
Fair Value	163,462	117,403
Available-for-sale, Amortized Cost [Abstract]
Amortized Cost	178,213	134,386
Available-for-sale, Fair Value [Abstract]
Fair Value	163,462	117,403
Securities held-to-maturity [Abstract]
Amortized Cost	198,650	184,241
Gross Unrealized Gains	0	0
Gross Unrealized Losses	18,645	18,573
Fair Value	180,005	165,668
Held-to-maturity, Amortized Cost [Abstract]
Amortized Cost	198,650	184,241
Held-to-maturity, Fair Value [Abstract]
Fair Value	180,005	165,668
Corporate notes and other
Securities available-for-sale [Abstract]
Amortized Cost	471,984	515,221
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax	72	41
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax	55,112	48,018
Fair Value	416,944	467,244
Available-for-sale, Amortized Cost [Abstract]
Amortized Cost	471,984	515,221
Available-for-sale, Fair Value [Abstract]
Fair Value	416,944	467,244
Securities held-to-maturity [Abstract]
Amortized Cost	86,561	88,527
Gross Unrealized Gains	0	0
Gross Unrealized Losses	11,186	9,918
Fair Value	75,375	78,609
Held-to-maturity, Amortized Cost [Abstract]
Amortized Cost	86,561	88,527
Held-to-maturity, Fair Value [Abstract]
Fair Value	$ 75,375	$ 78,609