Federal and State Income Taxes - Deferred Tax Assets and Deferred Tax Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets
Allowance for credit losses	$ 44,040	$ 31,698
Operating lease liabilities	12,551	11,127
Employee benefits	9,309	6,646
Deferred compensation	7,638	7,447
Acquisition fair market value adjustments	4,398	5,480
Net operating loss carryforwards	1,884	2,209
Other	2,262	3,891
Total gross deferred tax assets	82,082	68,498
Deferred tax liabilities
Available-for-sale debt securities	(48,505)	(13,652)
Intangibles	(14,671)	(16,469)
Depreciation of premises and equipment	(14,654)	(13,987)
Operating lease ROU assets	(11,830)	(10,506)
Deferred loan costs	(8,940)	(7,311)
Mortgage servicing rights	(2,268)	(411)
Other	(5,074)	(4,125)
Total gross deferred tax liabilities	(105,942)	(66,461)
Net deferred tax asset	$ (23,860)
Net deferred tax asset		$ 2,037