Investment Securities - Amortized Cost, Gross Unrealized Gains and Losses and Fair Value of Debt Securities Held to Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 3,766,838	$ 3,828,984
Gross Unrealized Gains	1,025	2,105
Gross Unrealized Losses	(488,915)	(501,619)
Fair Value	3,278,948	3,329,470
Allowance for Credit Losses	1,351	1,646	$ 1,508	$ 1,633	$ 1,165	$ 1,222
Net Carrying Value	3,765,487	3,827,338
U.S. Treasury securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	66,579	66,911
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(904)	(1,022)
Fair Value	65,675	65,889
Allowance for Credit Losses	0	0
Net Carrying Value	66,579	66,911
U.S. government agency securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	261,197	260,392
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(46,158)	(47,680)
Fair Value	215,039	212,712
Allowance for Credit Losses	0	0
Net Carrying Value	261,197	260,392
Obligations of states and state agencies
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	88,561	99,238
Gross Unrealized Gains	91	305
Gross Unrealized Losses	(5,112)	(3,869)
Fair Value	83,540	95,674
Allowance for Credit Losses	409	252
Net Carrying Value	88,152	98,986
Municipal bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	376,554	381,060
Gross Unrealized Gains	27	76
Gross Unrealized Losses	(21,130)	(23,615)
Fair Value	355,451	357,521
Allowance for Credit Losses	57	41
Net Carrying Value	376,497	381,019
Obligations of states and political subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	465,115	480,298
Gross Unrealized Gains	118	381
Gross Unrealized Losses	(26,242)	(27,484)
Fair Value	438,991	453,195
Allowance for Credit Losses	466	293
Net Carrying Value	464,649	480,005
Residential mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,861,227	2,909,106
Gross Unrealized Gains	906	1,723
Gross Unrealized Losses	(400,614)	(415,032)
Fair Value	2,461,519	2,495,797
Allowance for Credit Losses	0	0
Net Carrying Value	2,861,227	2,909,106
Trust preferred securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	37,052	37,043
Gross Unrealized Gains	1	1
Gross Unrealized Losses	(7,709)	(5,938)
Fair Value	29,344	31,106
Allowance for Credit Losses	559	888
Net Carrying Value	36,493	36,155
Corporate and other debt securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	75,668	75,234
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(7,288)	(4,463)
Fair Value	68,380	70,771
Allowance for Credit Losses	326	465
Net Carrying Value	$ 75,342	$ 74,769