Securities - Gross Unrealized Losses and Fair Value of Company's Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Fair Value less than 12 months	$ 512,531	$ 79,860
Unrealized losses less than 12 months	(10,172)	(294)
Fair value more than 12 months	1,458	1,245
Unrealized losses more than 12 months	(107)	(29)
Total fair value	513,989	81,105
Total unrealized losses	(10,279)	(323)
U.S. Treasury and federal agencies
Schedule of Available-for-sale Securities [Line Items]
Fair Value less than 12 months	37,697	17,215
Unrealized losses less than 12 months	(553)	(35)
Fair value more than 12 months	0	0
Unrealized losses more than 12 months	0	0
Total fair value	37,697	17,215
Total unrealized losses	(553)	(35)
State and municipal
Schedule of Available-for-sale Securities [Line Items]
Fair Value less than 12 months	459,377	56,287
Unrealized losses less than 12 months	(9,485)	(242)
Fair value more than 12 months	1,458	1,245
Unrealized losses more than 12 months	(107)	(29)
Total fair value	460,835	57,532
Total unrealized losses	(9,592)	(271)
Federal agency collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Fair Value less than 12 months	2,380	6,358
Unrealized losses less than 12 months	(5)	(17)
Fair value more than 12 months	0	0
Unrealized losses more than 12 months	0	0
Total fair value	2,380	6,358
Total unrealized losses	(5)	(17)
Federal agency mortgage-backed pools
Schedule of Available-for-sale Securities [Line Items]
Fair Value less than 12 months	12,081	0
Unrealized losses less than 12 months	(125)	0
Fair value more than 12 months	0	0
Unrealized losses more than 12 months	0	0
Total fair value	12,081	0
Total unrealized losses	(125)	$ 0
Corporate notes
Schedule of Available-for-sale Securities [Line Items]
Fair Value less than 12 months	996
Unrealized losses less than 12 months	(4)
Fair value more than 12 months	0
Unrealized losses more than 12 months	0
Total fair value	996
Total unrealized losses	$ (4)

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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