Income Taxes, Deferred Tax Assets and Liabilities Resulted in Deferred Taxes Table (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Gross deferred tax assets:
Allowance for loan losses	$ 88,967	$ 48,790
Allowance for other losses	16,347	7,236
Accrued liabilities	4,673	4,005
Deferred compensation	27,896	28,018
Benefit of tax loss and credit carryforwards	9,789	13,444
Nonaccrual interest	1,763	1,299
Basis Difference From Equity Securities and Other Investments	6,329	0
Net unrealized losses on pension and postretirement benefits	9,110	12,174
Other	997	970
Total deferred tax assets	165,871	115,936
Valuation allowance for deferred tax assets	(251)	(251)	$ (251)
Total deferred tax assets after valuation allowance	165,620	115,685
Gross deferred tax liabilities
Prepaid expenses	63,113	62,227
Goodwill	21,698	21,099
Mortgage banking activities	10,403	17,418
Deferred loan fee income	9,799	12,190
State deferred taxes	2,636	722
Lease financing	116	199
Bank premises and equipment	17,757	18,348
Purchase accounting	12,658	13,738
Deferred Tax Liability, Basis Difference From Equity Securities and Other Investments	0	2,285
Net unrealized gains on AFS securities	13,568	1,139
Other	1,049	1,156
Total deferred tax liabilities	152,797	150,521
Net deferred tax assets (liabilities)		$ (34,836)
Net deferred tax assets (liabilities)	$ 12,823