Investment Securities - Available for Sale and Held for Maturity Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021
Available-for-sale: [Abstract]
Amortized Cost	$ 1,571,215	$ 1,422,591
Gross Unrealized Gains	3,269	17,166
Gross Unrealized (Losses)	(107,534)	(18,335)
Fair Value	1,466,950	1,421,422
Held-to-maturity: [Abstract]
Held-to-maturity	2,998	7,030
Gross Unrealized Gains	0	5
Unrealized (Losses)	0	0
Fair Value	2,998	7,035	$ 7,035
U.S. Treasury Securities and Obligations of U.S. Government Corporations and Agencies
Available-for-sale: [Abstract]
Amortized Cost	264,466	208,598
Gross Unrealized Gains	37	80
Gross Unrealized (Losses)	(16,527)	(4,863)
Fair Value	247,976	203,815
Held-to-maturity: [Abstract]
Held-to-maturity		5,001
Gross Unrealized Gains		5
Unrealized (Losses)		0
Fair Value		5,006
Obligations of States and Political Subdivisions
Available-for-sale: [Abstract]
Amortized Cost	386,489	383,991
Gross Unrealized Gains	2,713	12,123
Gross Unrealized (Losses)	(30,523)	(657)
Fair Value	358,679	395,457
Mortgage-backed Securities: GSE Residential
Available-for-sale: [Abstract]
Amortized Cost	820,448	799,456
Gross Unrealized Gains	245	4,292
Gross Unrealized (Losses)	(59,166)	(12,710)
Fair Value	761,527	791,038
Other Securities
Available-for-sale: [Abstract]
Amortized Cost	99,812	30,546
Gross Unrealized Gains	274	671
Gross Unrealized (Losses)	(1,318)	(105)
Fair Value	98,768	31,112
Other Investments
Held-to-maturity: [Abstract]
Held-to-maturity	2,998	2,029
Gross Unrealized Gains	0	0
Unrealized (Losses)	0	0
Fair Value	$ 2,998	$ 2,029

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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