Loans, Loan Composition (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Loans and Leases Receivable Disclosure [Line Items]
Total loans	$ 20,931,460	$ 20,054,716
Commercial and industrial
Loans and Leases Receivable Disclosure [Line Items]
Total loans	6,534,660	6,489,014
Commercial real estate — owner occupied
Loans and Leases Receivable Disclosure [Line Items]
Total loans	827,064	897,724
Commercial and business lending
Loans and Leases Receivable Disclosure [Line Items]
Total loans	7,361,724	7,386,738
Commercial real estate — investor
Loans and Leases Receivable Disclosure [Line Items]
Total loans	3,345,536	3,574,732
Real estate construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans	1,552,135	1,432,497
Commercial real estate lending
Loans and Leases Receivable Disclosure [Line Items]
Total loans	4,897,671	5,007,229
Total commercial
Loans and Leases Receivable Disclosure [Line Items]
Total loans	12,259,395	12,393,967
Residential mortgage
Loans and Leases Receivable Disclosure [Line Items]
Total loans	7,408,471	6,332,327
Home equity
Loans and Leases Receivable Disclosure [Line Items]
Total loans	890,130	934,443
Other consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans	373,464	393,979
Total consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans	$ 8,672,065	$ 7,660,749