Investment Securities - Summary of available-for-sale securities - (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Marketable Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	$ 560,225	$ 277,323
Available-for-Sale Securities, Gross Unrealized Gains	18,624	6,332
Available-for-Sale Securities, Gross Unrealized Losses	(625)	(207)
Available-for-Sale Securities, Fair Value	578,224	283,448
Obligations of U.S. government corporations and agencies [Member]
Marketable Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	39,100	2,518
Available-for-Sale Securities, Gross Unrealized Gains	1,826	6
Available-for-Sale Securities, Fair Value	40,926	2,524
Mortgage-Backed Securities [Member]
Marketable Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	209,430	88,380
Available-for-Sale Securities, Gross Unrealized Gains	6,402	1,380
Available-for-Sale Securities, Gross Unrealized Losses	(193)	(113)
Available-for-Sale Securities, Fair Value	215,639	89,647
Collateralized mortgage obligations [Member]
Marketable Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	118,940	83,008
Available-for-Sale Securities, Gross Unrealized Gains	3,473	814
Available-for-Sale Securities, Gross Unrealized Losses	(129)	(85)
Available-for-Sale Securities, Fair Value	122,284	83,737
Corporate bonds [Member]
Marketable Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	29,971	12,011
Available-for-Sale Securities, Gross Unrealized Gains	223	90
Available-for-Sale Securities, Gross Unrealized Losses	(206)
Available-for-Sale Securities, Fair Value	29,988	12,101
Obligations of state and political subdivisions [Member]
Marketable Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	162,784	91,406
Available-for-Sale Securities, Gross Unrealized Gains	6,700	4,042
Available-for-Sale Securities, Gross Unrealized Losses	(97)	(9)
Available-for-Sale Securities, Fair Value	$ 169,387	$ 95,439

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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