Securities - Amortized Cost and Fair Value of Securities Available for Sale (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Amortized cost and fair value of securities available for sale
Amortized Cost	$ 1,515,958	$ 1,301,973
Gross Unrealized Gains	30,566	44,699
Gross Unrealized Losses	(10,483)	(3,215)
Fair Value	1,536,041	1,343,457
U.S. Treasury securities
Amortized cost and fair value of securities available for sale
Amortized Cost	3,028	7,047
Gross Unrealized Gains	22	32
Gross Unrealized Losses	0	0
Fair Value	3,050	7,079
Obligations of other U.S. Government agencies and corporations
Amortized cost and fair value of securities available for sale
Amortized Cost	1,001	1,003
Gross Unrealized Gains	3	6
Gross Unrealized Losses	0	0
Fair Value	1,004	1,009
Obligations of states and political subdivisions
Amortized cost and fair value of securities available for sale
Amortized Cost	321,156	291,231
Gross Unrealized Gains	9,344	14,015
Gross Unrealized Losses	(1,682)	(45)
Fair Value	328,818	305,201
Trust preferred securities
Amortized cost and fair value of securities available for sale
Amortized Cost		12,013
Gross Unrealized Gains		0
Gross Unrealized Losses		(3,001)
Fair Value		9,012
Other debt securities
Amortized cost and fair value of securities available for sale
Amortized Cost	61,113	62,771
Gross Unrealized Gains	2,126	2,909
Gross Unrealized Losses	(40)	(73)
Fair Value	63,199	65,607
Government agency mortgage backed securities \| Residential mortgage backed securities:
Amortized cost and fair value of securities available for sale
Amortized Cost	453,792	581,105
Gross Unrealized Gains	14,869	21,564
Gross Unrealized Losses	(2,206)	(23)
Fair Value	466,455	602,646
Government agency mortgage backed securities \| Commercial mortgage backed securities:
Amortized cost and fair value of securities available for sale
Amortized Cost	22,448	29,053
Gross Unrealized Gains	580	1,235
Gross Unrealized Losses	(23)	(1)
Fair Value	23,005	30,287
Government agency collateralized mortgage obligations \| Residential mortgage backed securities:
Amortized cost and fair value of securities available for sale
Amortized Cost	538,317	218,373
Gross Unrealized Gains	1,733	1,946
Gross Unrealized Losses	(4,718)	(51)
Fair Value	535,332	220,268
Government agency collateralized mortgage obligations \| Commercial mortgage backed securities:
Amortized cost and fair value of securities available for sale
Amortized Cost	115,103	99,377
Gross Unrealized Gains	1,889	2,992
Gross Unrealized Losses	(1,814)	(21)
Fair Value	$ 115,178	$ 102,348

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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Amortized cost of 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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