Loans Narrative (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Receivables [Abstract]
Recorded Investment, loans modified in troubled debt restructuring	$ 7,500	$ 10,138
Restructured Loans Subsequently Accruing	2,000
Ytd Restructured Loans Still On Nonaccrual	5,000
Net unaccreted purchase discount	15,000		$ 20,000
Unaccreted purchase discount, performing loans	14,000		18,000
Unaccreted purchase discount, nonperforming loans	1,000		2,000
Financing Receivable, Allowance for Credit Loss [Line Items]
Total allowance for loan losses	214,425		238,023	$ 265,880
Bank Mutual
Financing Receivable, Allowance for Credit Loss [Line Items]
Purchased credit-impaired loans	2,000		5,000
Huntington National Bank
Financing Receivable, Allowance for Credit Loss [Line Items]
Purchased credit-impaired loans	0
Oil and Gas
Financing Receivable, Allowance for Credit Loss [Line Items]
Total allowance for loan losses	$ 21,000		$ 12,000	$ 27,000
Percent of Loans	3.70%		1.60%