Loans Composition (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Loans and Leases Receivable Disclosure [Line Items]
Total loans	$ 23,148,359	$ 22,940,429
Commercial and industrial
Loans and Leases Receivable Disclosure [Line Items]
Total loans	7,587,597	7,398,044
Commercial real estate — owner occupied
Loans and Leases Receivable Disclosure [Line Items]
Total loans	932,393	920,443
Commercial and business lending
Loans and Leases Receivable Disclosure [Line Items]
Total loans	8,519,990	8,318,487
Commercial real estate — investor
Loans and Leases Receivable Disclosure [Line Items]
Total loans	3,809,253	3,751,554
Real estate construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans	1,273,782	1,335,031
Commercial real estate lending
Loans and Leases Receivable Disclosure [Line Items]
Total loans	5,083,035	5,086,585
Total commercial
Loans and Leases Receivable Disclosure [Line Items]
Total loans	13,603,025	13,405,072
Residential mortgage
Loans and Leases Receivable Disclosure [Line Items]
Total loans	8,323,846	8,277,712
Home equity
Loans and Leases Receivable Disclosure [Line Items]
Total loans	868,886	894,473
Other consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans	352,602	363,171
Total consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans	9,545,333	9,535,357
Bank Mutual
Loans and Leases Receivable Disclosure [Line Items]
Purchased credit-impaired loans	$ 5,000	$ 5,000