Securities, AFS Securities in Continuous Unrealized Loss Position (Details) $ in Thousands	Sep. 30, 2021 USD ($) Position	Dec. 31, 2020 USD ($) Position
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 657,563	$ 213,643
12 months or longer	154,869	800
Total	812,432	214,443
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	(8,405)	(2,170)
12 months or longer	(4,105)	(9)
Total	$ (12,510)	$ (2,179)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position	94	19
12 months or longer | Position	15	4
Total | Position	109	23
AIR on AFS debt securities	$ 3,300	$ 3,300
Federal Agency [Member]
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	101,674	148,537
12 months or longer	141,292	0
Total	242,966	148,537
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	(1,799)	(2,052)
12 months or longer	(3,697)	0
Total	$ (5,496)	$ (2,052)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position	7	10
12 months or longer | Position	9	0
Total | Position	16	10
State & Municipal [Member]
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 68,492
12 months or longer	0
Total	68,492
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	(753)
12 months or longer	0
Total	$ (753)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position	45
12 months or longer | Position	0
Total | Position	45
Mortgage-Backed [Member]
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 239,779	$ 47,269
12 months or longer	761	800
Total	240,540	48,069
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	(4,060)	(60)
12 months or longer	(8)	(9)
Total	$ (4,068)	$ (69)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position	18	3
12 months or longer | Position	4	4
Total | Position	22	7
Collateralized Mortgage Obligations [Member]
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 247,618	$ 17,837
12 months or longer	12,816	0
Total	260,434	17,837
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	(1,793)	(58)
12 months or longer	(400)	0
Total	$ (2,193)	$ (58)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position	24	6
12 months or longer | Position	2	0
Total | Position	26	6