Loans Composition (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Loans and Leases Receivable Disclosure [Line Items]
Total loans	$ 22,867,112	$ 20,784,991
Commercial and industrial
Loans and Leases Receivable Disclosure [Line Items]
Total loans	7,159,941	6,399,693
Commercial real estate — owner occupied
Loans and Leases Receivable Disclosure [Line Items]
Total loans	867,682	802,209
Commercial and business lending
Loans and Leases Receivable Disclosure [Line Items]
Total loans	8,027,622	7,201,902
Commercial real estate — investor
Loans and Leases Receivable Disclosure [Line Items]
Total loans	3,924,499	3,315,254
Real estate construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans	1,416,209	1,451,684
Commercial real estate lending
Loans and Leases Receivable Disclosure [Line Items]
Total loans	5,340,708	4,766,938
Total commercial
Loans and Leases Receivable Disclosure [Line Items]
Total loans	13,368,330	11,968,840
Residential mortgage
Loans and Leases Receivable Disclosure [Line Items]
Total loans	8,227,649	7,546,534
Home equity
Loans and Leases Receivable Disclosure [Line Items]
Total loans	901,275	883,804
Other consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans	369,858	385,813
Total consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans	9,498,782	$ 8,816,151
Bank Mutual
Loans and Leases Receivable Disclosure [Line Items]
Purchased credit-impaired loans	$ 13,000