Debt Securities - Amortized Cost, Gross Unrealized Gains and Losses and Fair Value of Investment Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Available-for-sale
Amortized Cost	$ 5,930,103	$ 9,175,423
Gross Unrealized Gains	1,085	68,117
Gross Unrealized Losses	(623,881)	(72,691)
Fair Value	5,307,307	9,170,849
Held-to-maturity
Amortized Cost	3,715,052	1,199,164
Gross Unrealized Gains	1,045	22,878
Gross Unrealized Losses	(441,305)	(1,159)
Fair Value	3,274,792	1,220,883
Total debt securities
Amortized Cost	9,645,155	10,374,587
Gross Unrealized Gains	2,130	90,995
Gross Unrealized Losses	(1,065,186)	(73,850)
Fair Value	8,582,099	10,391,732
U.S. government and federal agency
Available-for-sale
Amortized Cost	487,320	1,356,171
Gross Unrealized Gains	23	174
Gross Unrealized Losses	(42,616)	(9,596)
Fair Value	444,727	1,346,749
Held-to-maturity
Amortized Cost	846,046
Gross Unrealized Gains	0
Gross Unrealized Losses	(83,796)
Fair Value	762,250
U.S. government sponsored enterprises
Available-for-sale
Amortized Cost	320,157	241,687
Gross Unrealized Gains	0	2
Gross Unrealized Losses	(32,793)	(996)
Fair Value	287,364	240,693
State and local governments
Available-for-sale
Amortized Cost	137,033	461,414
Gross Unrealized Gains	709	27,567
Gross Unrealized Losses	(4,749)	(123)
Fair Value	132,993	488,858
Held-to-maturity
Amortized Cost	1,682,640	1,199,164
Gross Unrealized Gains	1,045	22,878
Gross Unrealized Losses	(248,233)	(1,159)
Fair Value	1,435,452	1,220,883
Corporate bonds
Available-for-sale
Amortized Cost	27,101	175,697
Gross Unrealized Gains	0	5,072
Gross Unrealized Losses	(992)	(17)
Fair Value	26,109	180,752
Residential mortgage-backed securities
Available-for-sale
Amortized Cost	3,706,427	5,744,505
Gross Unrealized Gains	6	9,420
Gross Unrealized Losses	(439,092)	(54,266)
Fair Value	3,267,341	5,699,659
Held-to-maturity
Amortized Cost	1,186,366
Gross Unrealized Gains	0
Gross Unrealized Losses	(109,276)
Fair Value	1,077,090
Commercial mortgage-backed securities
Available-for-sale
Amortized Cost	1,252,065	1,195,949
Gross Unrealized Gains	347	25,882
Gross Unrealized Losses	(103,639)	(7,693)
Fair Value	$ 1,148,773	$ 1,214,138