Investments - Schedule of Available-for-sale and Held-to-Maturity Securities Reconciliation (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Held-to-maturity [Abstract]
Amortized Cost	$ 439,112	$ 488,059
Gross Unrealized Gains	7,465	13,960
Gross Unrealized Losses	(1,952)	(496)
Allowance for Credit Losses	(640)	(449)
Fair Value	444,625	501,523
Debt Securities, Held-To-Maturity, Net Of Allowance For Credit Losses	438,472	487,610
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	1,211,293	882,682
Gross Unrealized Gains	16,803	30,104
Gross Unrealized Losses	(8,282)	(357)
Securities available-for-sale	1,219,814	912,429
Obligations of U.S. Government-sponsored enterprises
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	115,567	14,978
Gross Unrealized Gains	35	186
Gross Unrealized Losses	(665)	(3)
Securities available-for-sale	114,937	15,161
Obligations of states and political subdivisions
Debt Securities, Held-to-maturity [Abstract]
Amortized Cost	238,031	248,324
Gross Unrealized Gains	1,302	2,814
Gross Unrealized Losses	(1,634)	0
Fair Value	237,699	251,138
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	516,659	335,271
Gross Unrealized Gains	3,641	8,994
Gross Unrealized Losses	(4,884)	(33)
Securities available-for-sale	515,416	344,232
Agency mortgage-backed securities
Debt Securities, Held-to-maturity [Abstract]
Amortized Cost	74,972	112,742
Gross Unrealized Gains	1,303	2,295
Gross Unrealized Losses	(318)	(496)
Fair Value	75,957	114,541
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	496,330	506,703
Gross Unrealized Gains	12,166	20,190
Gross Unrealized Losses	(2,730)	(321)
Securities available-for-sale	505,766	526,572
U.S. Treasury bills
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	70,987	10,980
Gross Unrealized Gains	308	486
Gross Unrealized Losses	(3)	0
Securities available-for-sale	71,292	11,466
Corporate debt securities
Debt Securities, Held-to-maturity [Abstract]
Amortized Cost	126,109	126,993
Gross Unrealized Gains	4,860	8,851
Gross Unrealized Losses	0	0
Fair Value	130,969	135,844
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	11,750	14,750
Gross Unrealized Gains	653	248
Gross Unrealized Losses	0	0
Securities available-for-sale	$ 12,403	$ 14,998

Debt Securities, Held-To-Maturity, Net Of Allowance For Credit Losses

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