Securities - Schedule of Debt Securities Components (Details) - USD ($) $ in Thousands		Sep. 30, 2021	Dec. 31, 2020
Available-for-sale [Abstract]
Amortized Cost		$ 2,650,237	$ 2,437,513
Gross unrealized gains		110,187	150,074
Gross unrealized losses		7,320	282
Securities available for sale, at estimated fair value		2,753,104	2,587,305
HELD TO MATURITY
Amortized cost		92,479	108,998
Gross unrealized gains		5,556	9,200
Gross unrealized losses		0	0
Estimated Fair Value		98,035	118,198
US Treasury Securities
Available-for-sale [Abstract]
Amortized Cost		42,806
Gross unrealized gains		741
Gross unrealized losses		0
Securities available for sale, at estimated fair value		43,547
State and political subdivisions
Available-for-sale [Abstract]
Amortized Cost		1,890,814	1,475,030
Gross unrealized gains		83,140	105,601
Gross unrealized losses		6,477	37
Securities available for sale, at estimated fair value		1,967,477	1,580,594
HELD TO MATURITY
Amortized cost		788	907
Gross unrealized gains		3	13
Gross unrealized losses		0	0
Estimated Fair Value		791	920
Corporate bonds and other
Available-for-sale [Abstract]
Amortized Cost		117,332	77,224
Gross unrealized gains		2,563	1,053
Gross unrealized losses		196	22
Securities available for sale, at estimated fair value		119,699	78,255
Residential
Available-for-sale [Abstract]
Amortized Cost	[1]	493,505	771,409
Gross unrealized gains	[1]	20,943	38,674
Gross unrealized losses	[1]	370	73
Securities available for sale, at estimated fair value	[1]	514,078	810,010
HELD TO MATURITY
Amortized cost	[1]	40,128	47,948
Gross unrealized gains	[1]	2,616	4,187
Gross unrealized losses	[1]	0	0
Estimated Fair Value	[1]	42,744	52,135
Commercial
Available-for-sale [Abstract]
Amortized Cost	[1]	105,780	113,850
Gross unrealized gains	[1]	2,800	4,746
Gross unrealized losses	[1]	277	150
Securities available for sale, at estimated fair value	[1]	108,303	118,446
HELD TO MATURITY
Amortized cost	[1]	51,563	60,143
Gross unrealized gains	[1]	2,937	5,000
Gross unrealized losses	[1]	0	0
Estimated Fair Value	[1]	$ 54,500	$ 65,143

[1] All MBS are issued and/or guaranteed by U.S. government agencies or U.S. GSEs.