Income Taxes, Deferred Tax Assets and Liabilities Resulted in Deferred Taxes Table (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Gross deferred tax assets:
Allowance for loan losses	$ 61,143	$ 66,377
Allowance for other losses	8,304	7,095
Accrued liabilities	3,736	3,884
Deferred compensation	24,754	20,015
Benefit of tax loss and credit carryforwards	10,126	8,438
Nonaccrual interest	1,666	1,619
Net unrealized losses on available-for-sale securities	25,731	15,968
Net unrealized losses on pension and postretirement benefits	16,640	9,928
Other	1,916	4,435
Total deferred tax assets	154,015	137,759
Valuation allowance for deferred tax assets	(251)	(269)	$ 0
Total deferred tax assets after valuation allowance	153,764	137,490
Gross deferred tax liabilities
Prepaid expenses	61,250	49,695
Goodwill	20,178	19,144
Mortgage banking activities	17,428	10,949
Deferred loan fee income	11,892	11,467
State deferred taxes	518	2,001
Lease financing	410	535
Bank premises and equipment	18,655	5,063
Purchase accounting	12,414	5,015
Other	684	304
Total deferred tax liabilities	143,429	104,173
Net deferred tax assets	$ 10,335	$ 33,317