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Securities - Fair Values and Amortized Costs Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-Sale, Amortized Cost	$ 679,473	$ 768,427
Debt Securities, Available-for-Sale, Gross Unrealized Gains	35,448	11,659
Debt Securities, Available-for-Sale, Gross Unrealized Losses	(1)	(953)
Debt Securities, Available-for-Sale, Fair Value	714,920	779,133
Marketable equity securities	3,249	5,150
Total Securities	718,169	784,283
Interest receivable	3,000	3,400
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-Sale, Amortized Cost	9,977	9,969
Debt Securities, Available-for-Sale, Gross Unrealized Gains	346	71
Debt Securities, Available-for-Sale, Gross Unrealized Losses	0
Debt Securities, Available-for-Sale, Fair Value	10,323	10,040
Obligations of U.S. government corporations and agencies
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-Sale, Amortized Cost	88,809	155,969
Debt Securities, Available-for-Sale, Gross Unrealized Gains	4,542	1,773
Debt Securities, Available-for-Sale, Gross Unrealized Losses	0	(45)
Debt Securities, Available-for-Sale, Fair Value	93,351	157,697
Collateralized mortgage obligations of U.S. government corporations and agencies
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-Sale, Amortized Cost	175,516	186,879
Debt Securities, Available-for-Sale, Gross Unrealized Gains	7,516	2,773
Debt Securities, Available-for-Sale, Gross Unrealized Losses	0	(304)
Debt Securities, Available-for-Sale, Fair Value	183,032	189,348
Residential mortgage-backed securities of U.S. government corporations and agencies
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-Sale, Amortized Cost	16,578	22,120
Debt Securities, Available-for-Sale, Gross Unrealized Gains	774	321
Debt Securities, Available-for-Sale, Gross Unrealized Losses	0	(23)
Debt Securities, Available-for-Sale, Fair Value	17,352	22,418
Commercial mortgage-backed securities of U.S. government corporations and agencies
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-Sale, Amortized Cost	265,202	273,771
Debt Securities, Available-for-Sale, Gross Unrealized Gains	15,022	2,680
Debt Securities, Available-for-Sale, Gross Unrealized Losses	0	(581)
Debt Securities, Available-for-Sale, Fair Value	280,224	275,870
Corporate obligations
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-Sale, Amortized Cost	4,023	7,603
Debt Securities, Available-for-Sale, Gross Unrealized Gains	5	24
Debt Securities, Available-for-Sale, Gross Unrealized Losses	(1)	0
Debt Securities, Available-for-Sale, Fair Value	4,027	7,627
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-Sale, Amortized Cost	119,368	112,116
Debt Securities, Available-for-Sale, Gross Unrealized Gains	7,243	4,017
Debt Securities, Available-for-Sale, Gross Unrealized Losses	0	0
Debt Securities, Available-for-Sale, Fair Value	$ 126,611	$ 116,133

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