Loans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses	$ 238,023	$ 265,880	$ 278,335
Financing Receivable, Modifications, Post-Modification Recorded Investment	11,429	9,426	9,270
Restructured Loans Subsequently Accruing	3,000
Ytd Restructured Loans Still On Nonaccrual	8,000
Loans and Leases Receivable, Impaired, Commitment to Lend	6,000
UnaccretedPurchaseDiscount	20,000
UnaccretedPurchaseDiscount_PerformingLoans	18,000
UnaccretedPurchaseDiscount_NonPerformingLoans	2,000
Oil and Gas Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses	$ 12,000	$ 27,000	$ 38,000
Percent of Loans	1.62%
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	$ 5,000