Investment Securities - Amortized Cost Basis, Unrealized Gains and Losses and Fair value of HTM Debt Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
HTM debt securities:
Amortized Cost	$ 2,465,133	$ 2,490,848
Gross Unrealized Gains	32	195
Gross Unrealized Losses	422,253	395,423
Fair Value	2,042,912	2,095,620
U.S. Treasuries
HTM debt securities:
Amortized Cost	19,872	19,864
Gross Unrealized Gains	0	0
Gross Unrealized Losses	2,093	1,914
Fair Value	17,779	17,950
U.S. Government agencies & GSEs
HTM debt securities:
Amortized Cost	99,052	99,052
Gross Unrealized Gains	0	0
Gross Unrealized Losses	16,673	15,689
Fair Value	82,379	83,363
State and political subdivisions
HTM debt securities:
Amortized Cost	292,236	292,705
Gross Unrealized Gains	23	171
Gross Unrealized Losses	52,802	50,437
Fair Value	239,457	242,439
Residential MBS, Agency & GSEs
HTM debt securities:
Amortized Cost	1,360,395	1,383,294
Gross Unrealized Gains	9	24
Gross Unrealized Losses	223,439	206,344
Fair Value	1,136,965	1,176,974
Commercial MBS, Agency & GSEs
HTM debt securities:
Amortized Cost	678,578	680,933
Gross Unrealized Gains	0	0
Gross Unrealized Losses	124,464	118,539
Fair Value	554,114	562,394
Supranational entities
HTM debt securities:
Amortized Cost	15,000	15,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	2,782	2,500
Fair Value	$ 12,218	$ 12,500