Income Taxes, Deferred Tax Assets and Liabilities Resulted in Deferred Taxes Table (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Gross deferred tax assets:
Allowance for loan losses	$ 48,790,000	$ 61,143,000
Allowance for other losses	7,236,000	8,304,000
Accrued liabilities	4,005,000	3,736,000
Deferred compensation	28,018,000	24,754,000
Benefit of tax loss and credit carryforwards	13,444,000	10,126,000
Nonaccrual interest	1,299,000	1,666,000
Net unrealized losses on available-for-sale securities	0	25,731,000
Net unrealized losses on pension and postretirement benefits	12,174,000	16,640,000
Other	3,495,000	1,916,000
Total deferred tax assets	118,461,000	154,015,000
Valuation allowance for deferred tax assets	(251,000)	(251,000)	$ (269,000)
Total deferred tax assets after valuation allowance	118,211,000	153,764,000
Gross deferred tax liabilities
Prepaid expenses	62,227,000	61,250,000
Goodwill	21,099,000	20,178,000
Mortgage banking activities	17,418,000	17,428,000
Deferred loan fee income	12,190,000	11,892,000
State deferred taxes	722,000	518,000
Lease financing	199,000	410,000
Bank premises and equipment	18,348,000	18,655,000
Purchase accounting	13,738,000	12,414,000
Deferred gains from equity securities and other investments	4,810,000	0
Net unrealized gains on available-for-sale securities	1,139,000	0
Other	1,156,000	684,000
Total deferred tax liabilities	153,045,000	143,429,000
Deferred Tax Liabilities, Net	$ (34,836,000)
Net deferred tax assets (liabilities)		$ 10,335,000