Loans Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Receivables [Abstract]
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 4,035	$ 35,020
Restructured Loans Subsequently Accruing_String	less than $1 million
Ytd Restructured Loans Still On Nonaccrual	$ 4,000	4,000
UnaccretedPurchaseDiscount		32,000
UnaccretedPurchaseDiscount_PerformingLoans	26,000	26,000
UnaccretedPurchaseDiscount_NonPerformingLoans	7,000	7,000
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses	252,601	252,601		$ 265,880	$ 278,335
Oil and Gas Portfolio Segment
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses	$ 17,000	$ 17,000		$ 27,000	$ 38,000
Percent of loans	2.50%	2.50%
Bank Mutual [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Net of Deferred Income, Purchased Credit Impaired Loans And Covered Loans	$ 16,000	$ 16,000