Loans, Loan Composition (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Loans and Leases Receivable Disclosure [Line Items]
Total loans	$ 20,783,069	$ 20,054,716
Commercial and industrial
Loans and Leases Receivable Disclosure [Line Items]
Total loans	6,571,000	6,489,014
Commercial real estate — owner occupied
Loans and Leases Receivable Disclosure [Line Items]
Total loans	845,336	897,724
Commercial and business lending
Loans and Leases Receivable Disclosure [Line Items]
Total loans	7,416,336	7,386,738
Commercial real estate — investor
Loans and Leases Receivable Disclosure [Line Items]
Total loans	3,329,585	3,574,732
Real estate construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans	1,651,805	1,432,497
Commercial real estate lending
Loans and Leases Receivable Disclosure [Line Items]
Total loans	4,981,390	5,007,229
Total commercial
Loans and Leases Receivable Disclosure [Line Items]
Total loans	12,397,726	12,393,967
Residential mortgage
Loans and Leases Receivable Disclosure [Line Items]
Total loans	7,115,457	6,332,327
Home equity
Loans and Leases Receivable Disclosure [Line Items]
Total loans	897,111	934,443
Other consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans	372,775	393,979
Total consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans	$ 8,385,343	$ 7,660,749