Securities - Amortized Cost and Fair Value of Securities Available for Sale (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Amortized cost and fair value of securities available for sale
Amortized Cost	$ 1,263,898	$ 1,276,871
Gross Unrealized Gains	45,083	18,620
Gross Unrealized Losses	(5,487)	(4,878)
Allowance for Credit Losses	0
Fair Value	1,303,494	1,290,613
U.S. Treasury securities
Amortized cost and fair value of securities available for sale
Amortized Cost	7,586	498
Gross Unrealized Gains	53	1
Gross Unrealized Losses	0	0
Allowance for Credit Losses	0
Fair Value	7,639	499
Obligations of other U.S. Government agencies and corporations
Amortized cost and fair value of securities available for sale
Amortized Cost	2,509	2,518
Gross Unrealized Gains	21	16
Gross Unrealized Losses	0	(3)
Allowance for Credit Losses	0
Fair Value	2,530	2,531
Obligations of states and political subdivisions
Amortized cost and fair value of securities available for sale
Amortized Cost	263,618	218,362
Gross Unrealized Gains	10,170	5,134
Gross Unrealized Losses	(817)	(365)
Allowance for Credit Losses	0
Fair Value	272,971	223,131
Trust preferred securities
Amortized cost and fair value of securities available for sale
Amortized Cost	12,068	12,153
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(4,389)	(2,167)
Allowance for Credit Losses	0
Fair Value	7,679	9,986
Other debt securities
Amortized cost and fair value of securities available for sale
Amortized Cost	58,642	55,364
Gross Unrealized Gains	2,440	1,133
Gross Unrealized Losses	(212)	(132)
Allowance for Credit Losses	0
Fair Value	60,870	56,365
Government agency mortgage backed securities \| Residential mortgage backed securities:
Amortized cost and fair value of securities available for sale
Amortized Cost	659,279	708,970
Gross Unrealized Gains	24,887	8,951
Gross Unrealized Losses	(1)	(1,816)
Allowance for Credit Losses	0
Fair Value	684,165	716,105
Government agency mortgage backed securities \| Commercial mortgage backed securities:
Amortized cost and fair value of securities available for sale
Amortized Cost	32,706	30,372
Gross Unrealized Gains	1,712	659
Gross Unrealized Losses	(1)	(24)
Allowance for Credit Losses	0
Fair Value	34,417	31,007
Government agency collateralized mortgage obligations \| Residential mortgage backed securities:
Amortized cost and fair value of securities available for sale
Amortized Cost	137,181	172,178
Gross Unrealized Gains	2,366	1,322
Gross Unrealized Losses	(27)	(262)
Allowance for Credit Losses	0
Fair Value	139,520	173,238
Government agency collateralized mortgage obligations \| Commercial mortgage backed securities:
Amortized cost and fair value of securities available for sale
Amortized Cost	90,309	76,456
Gross Unrealized Gains	3,434	1,404
Gross Unrealized Losses	(40)	(109)
Allowance for Credit Losses	0
Fair Value	$ 93,703	$ 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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Amount of allowance for credit loss 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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