Income Taxes, Deferred Tax Assets and Liabilities Resulted in Deferred Taxes Table (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Gross deferred tax assets:
Allowance for loan losses	$ 66,377	$ 100,891
Allowance for other losses	7,095	11,080
Accrued liabilities	3,884	5,969
Deferred compensation	20,015	33,169
Benefit of tax loss and credit carryforwards	8,438	7,882
Nonaccrual interest	1,619	1,085
Net unrealized losses on available-for-sale securities	15,968	16,980
Net unrealized losses on pension and postretirement benefits	9,928	21,218
Other	3,954	8,128
Total deferred tax assets	137,278	206,402
Valuation allowance for deferred tax assets	(269)	0	$ 0
Total deferred tax assets after valuation allowance	137,009	206,402
Gross deferred tax liabilities
Prepaid expenses	49,695	70,943
Goodwill	19,144	27,365
Mortgage banking activities	10,949	17,569
Deferred loan fee income	11,467	16,474
State deferred taxes	2,001	3,800
Lease financing	535	1,975
Bank premises and equipment	5,063	7,698
Other	4,838	8,594
Total deferred tax liabilities	103,692	154,418
Net deferred tax assets	$ 33,317	$ 51,984