Securities - Gross Unrealized Losses and Fair Value by Investment Category (Details) $ in Thousands	Mar. 31, 2021 USD ($) security	Dec. 31, 2020 USD ($) security
Available for Sale:
Number of positions, Less than 12 Months | security	89	21
Fair Value, Less than 12 Months	$ 637,692	$ 75,359
Unrealized Losses, Less than 12 Months	$ (10,432)	$ (211)
Number of positions, 12 Months or More | security	3	4
Fair value, 12 Months or More	$ 3,142	$ 10,037
Unrealized Losses, 12 Months or More	$ (51)	$ (3,004)
Number of positions | security	92	25
Fair Value	$ 640,834	$ 85,396
Unrealized Losses	$ (10,483)	$ (3,215)
Obligations of states and political subdivisions
Available for Sale:
Number of positions, Less than 12 Months | security	41	6
Fair Value, Less than 12 Months	$ 97,392	$ 9,403
Unrealized Losses, Less than 12 Months	$ (1,634)	$ (45)
Number of positions, 12 Months or More | security	1	0
Fair value, 12 Months or More	$ 2,133	$ 0
Unrealized Losses, 12 Months or More	$ (48)	$ 0
Number of positions | security	42	6
Fair Value	$ 99,525	$ 9,403
Unrealized Losses	$ (1,682)	$ (45)
Trust preferred securities
Available for Sale:
Number of positions, Less than 12 Months | security		0
Fair Value, Less than 12 Months		$ 0
Unrealized Losses, Less than 12 Months		$ 0
Number of positions, 12 Months or More | security		2
Fair value, 12 Months or More		$ 9,012
Unrealized Losses, 12 Months or More		$ (3,001)
Number of positions | security		2
Fair Value		$ 9,012
Unrealized Losses		$ (3,001)
Other debt securities
Available for Sale:
Number of positions, Less than 12 Months | security	6	4
Fair Value, Less than 12 Months	$ 9,042	$ 3,330
Unrealized Losses, Less than 12 Months	$ (37)	$ (70)
Number of positions, 12 Months or More | security	1	1
Fair value, 12 Months or More	$ 557	$ 566
Unrealized Losses, 12 Months or More	$ (3)	$ (3)
Number of positions | security	7	5
Fair Value	$ 9,599	$ 3,896
Unrealized Losses	$ (40)	$ (73)
Government agency mortgage backed securities | Residential mortgage backed securities:
Available for Sale:
Number of positions, Less than 12 Months | security	14	2
Fair Value, Less than 12 Months	$ 119,498	$ 19,755
Unrealized Losses, Less than 12 Months	$ (2,206)	$ (23)
Number of positions, 12 Months or More | security	0	0
Fair value, 12 Months or More	$ 0	$ 0
Unrealized Losses, 12 Months or More	$ 0	$ 0
Number of positions | security	14	2
Fair Value	$ 119,498	$ 19,755
Unrealized Losses	$ (2,206)	$ (23)
Government agency mortgage backed securities | Commercial mortgage backed securities:
Available for Sale:
Number of positions, Less than 12 Months | security	1	1
Fair Value, Less than 12 Months	$ 1,082	$ 1,538
Unrealized Losses, Less than 12 Months	$ (23)	$ (1)
Number of positions, 12 Months or More | security	1	1
Fair value, 12 Months or More	$ 452	$ 459
Unrealized Losses, 12 Months or More	$ 0	$ 0
Number of positions | security	2	2
Fair Value	$ 1,534	$ 1,997
Unrealized Losses	$ (23)	$ (1)
Government agency collateralized mortgage obligations | Residential mortgage backed securities:
Available for Sale:
Number of positions, Less than 12 Months | security	17	5
Fair Value, Less than 12 Months	$ 351,956	$ 27,143
Unrealized Losses, Less than 12 Months	$ (4,718)	$ (51)
Number of positions, 12 Months or More | security	0	0
Fair value, 12 Months or More	$ 0	$ 0
Unrealized Losses, 12 Months or More	$ 0	$ 0
Number of positions | security	17	5
Fair Value	$ 351,956	$ 27,143
Unrealized Losses	$ (4,718)	$ (51)
Government agency collateralized mortgage obligations | Commercial mortgage backed securities:
Available for Sale:
Number of positions, Less than 12 Months | security	10	3
Fair Value, Less than 12 Months	$ 58,722	$ 14,190
Unrealized Losses, Less than 12 Months	$ (1,814)	$ (21)
Number of positions, 12 Months or More | security	0	0
Fair value, 12 Months or More	$ 0	$ 0
Unrealized Losses, 12 Months or More	$ 0	$ 0
Number of positions | security	10	3
Fair Value	$ 58,722	$ 14,190
Unrealized Losses	$ (1,814)	$ (21)