Loans, Loan Composition (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Loans and Leases Receivable Disclosure [Line Items]
Total loans	$ 20,147,683	$ 20,054,716
Commercial and industrial
Loans and Leases Receivable Disclosure [Line Items]
Total loans	6,300,646	6,489,014
Commercial real estate — owner occupied
Loans and Leases Receivable Disclosure [Line Items]
Total loans	878,391	897,724
Commercial and business lending
Loans and Leases Receivable Disclosure [Line Items]
Total loans	7,179,037	7,386,738
Commercial real estate — investor
Loans and Leases Receivable Disclosure [Line Items]
Total loans	3,415,355	3,574,732
Real estate construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans	1,553,205	1,432,497
Commercial real estate lending
Loans and Leases Receivable Disclosure [Line Items]
Total loans	4,968,560	5,007,229
Total commercial
Loans and Leases Receivable Disclosure [Line Items]
Total loans	12,147,597	12,393,967
Residential mortgage
Loans and Leases Receivable Disclosure [Line Items]
Total loans	6,715,282	6,332,327
Home equity
Loans and Leases Receivable Disclosure [Line Items]
Total loans	911,969	934,443
Other consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans	372,835	393,979
Total consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans	$ 8,000,086	$ 7,660,749