Securities - Amortized Cost and Fair Value, Available for Sale (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Cash and Cash Equivalents [Line Items]
Amortized Cost	$ 1,301,973	$ 1,276,871
Gross Unrealized Gains	44,699	18,620
Gross Unrealized Losses	(3,215)	(4,878)
Fair Value	1,343,457	1,290,613
U.S. Treasury securities
Cash and Cash Equivalents [Line Items]
Amortized Cost	7,047	498
Gross Unrealized Gains	32	1
Gross Unrealized Losses	0	0
Fair Value	7,079	499
Obligations of other U.S. Government agencies and corporations
Cash and Cash Equivalents [Line Items]
Amortized Cost	1,003	2,518
Gross Unrealized Gains	6	16
Gross Unrealized Losses	0	(3)
Fair Value	1,009	2,531
Obligations of states and political subdivisions
Cash and Cash Equivalents [Line Items]
Amortized Cost	291,231	218,362
Gross Unrealized Gains	14,015	5,134
Gross Unrealized Losses	(45)	(365)
Fair Value	305,201	223,131
Trust preferred securities
Cash and Cash Equivalents [Line Items]
Amortized Cost	12,013	12,153
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(3,001)	(2,167)
Fair Value	9,012	9,986
Other debt securities
Cash and Cash Equivalents [Line Items]
Amortized Cost	62,771	55,364
Gross Unrealized Gains	2,909	1,133
Gross Unrealized Losses	(73)	(132)
Fair Value	65,607	56,365
Government agency mortgage backed securities \| Residential mortgage backed securities
Cash and Cash Equivalents [Line Items]
Amortized Cost	581,105	708,970
Gross Unrealized Gains	21,564	8,951
Gross Unrealized Losses	(23)	(1,816)
Fair Value	602,646	716,105
Government agency mortgage backed securities \| Commercial mortgage backed securities
Cash and Cash Equivalents [Line Items]
Amortized Cost	29,053	30,372
Gross Unrealized Gains	1,235	659
Gross Unrealized Losses	(1)	(24)
Fair Value	30,287	31,007
Government agency collateralized mortgage obligations \| Residential mortgage backed securities
Cash and Cash Equivalents [Line Items]
Amortized Cost	218,373	172,178
Gross Unrealized Gains	1,946	1,322
Gross Unrealized Losses	(51)	(262)
Fair Value	220,268	173,238
Government agency collateralized mortgage obligations \| Commercial mortgage backed securities
Cash and Cash Equivalents [Line Items]
Amortized Cost	99,377	76,456
Gross Unrealized Gains	2,992	1,404
Gross Unrealized Losses	(21)	(109)
Fair Value	$ 102,348	$ 77,751

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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