Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended									12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current expense:
Federal										$ 22,479	$ 18,076	$ 27,168
State										8,910	9,807	4,117
Deferred expense:
Federal										(380)	5,068	11,583
State										476	2,048	2,517
Total income tax expense	$ 7,146	$ 8,052	$ 6,702	$ 9,585	$ 8,891	$ 9,081	$ 8,749	$ 8,278		$ 31,485	$ 34,999	$ 45,385
Reconciliation of federal and state income taxes at statutory rates to the income taxes included in the statements of operations
Income tax at statutory rate (as a percent)										21.00%	21.00%	35.00%
TCJA (as a percent)												7.50%
Tax-exempt interest, net (as a percent)										(1.70%)	(1.30%)	(2.10%)
Stock incentive (as a percent)										(0.10%)	(0.30%)	(0.50%)
State income taxes, net (as a percent)										5.50%	7.30%	4.00%
Income on bank owned life insurance (as a percent)										(0.90%)	(0.60%)	(0.90%)
Tax credit investments										(1.30%)
Other, net (as a percent)										0.90%		(1.00%)
Total (as a percent)										23.40%	26.10%	42.00%
Deferred tax assets:
Unrealized losses on debt securities available for sale					2,716						$ 2,716
Allowance for loan losses	15,416				14,885					$ 15,416	14,885
Stock-based compensation	2,069				2,208					2,069	2,208
Deferred compensation	166				1,454					166	1,454
Affordable housing partnerships and other investments	777				691					777	691
Purchase accounting adjustments	11,301				4,563					11,301	4,563
Accrued vacation	827				744					827	744
Lease liability	2,650									2,650
Employee costs	1,048				260					1,048	260
Other	809				1,095					809	1,095
Total	35,063				28,616					35,063	28,616
Deferred tax liabilities:
Unrealized gains on debt securities available for sale	(6,032)									(6,032)
Basis in premises and equipment	(4,222)				(1,213)					(4,222)	(1,213)
Affordable housing partnerships and other investments	(1,411)				(1,868)					(1,411)	(1,868)
Purchase accounting adjustments	(1,023)				(1,102)					(1,023)	(1,102)
Mortgage servicing assets	(3,717)				(1,159)					(3,717)	(1,159)
Basis in core deposit and customer intangible assets	(17,120)				(9,299)					(17,120)	(9,299)
Deferred loan origination costs	(1,730)				(1,593)					(1,730)	(1,593)
Lease right of use asset	(2,633)									(2,633)
Unrealized gain on equity securities	(593)				(662)					(593)	(662)
Other	(508)				(322)					(508)	(322)
Deferred tax liabilities	(38,989)				(17,218)					(38,989)	(17,218)
Net operating loss carryforward, net of valuation allowance					33						33
Net deferred tax assets	(3,926)									(3,926)
Net deferred tax (liability) asset					11,431						11,431
Non-cash charge due to revaluation of Company's net deferred tax position following the enactment of the TCJA									$ 8,100
Operating loss carryforwards	0									0
Valuation allowance, deferred tax assets	$ 0				$ 0					$ 0	$ 0