Loans, Loan Composition (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Loans and Leases Receivable Disclosure [Line Items]
Total loans	$ 19,227,240	$ 18,714,343
Commercial and industrial
Loans and Leases Receivable Disclosure [Line Items]
Total loans	6,511,648	6,190,683
Commercial real estate — owner occupied
Loans and Leases Receivable Disclosure [Line Items]
Total loans	917,285	918,212
Commercial and business lending
Loans and Leases Receivable Disclosure [Line Items]
Total loans	7,428,933	7,108,895
Commercial real estate — investor
Loans and Leases Receivable Disclosure [Line Items]
Total loans	3,276,733	3,234,266
Real estate construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans	1,184,398	1,162,145
Commercial real estate lending
Loans and Leases Receivable Disclosure [Line Items]
Total loans	4,461,131	4,396,411
Total commercial
Loans and Leases Receivable Disclosure [Line Items]
Total loans	11,890,064	11,505,306
Residential mortgage
Loans and Leases Receivable Disclosure [Line Items]
Total loans	5,944,457	5,783,267
Home equity
Loans and Leases Receivable Disclosure [Line Items]
Total loans	982,994	1,005,802
Other consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans	409,725	419,968
Total consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans	$ 7,337,176	$ 7,209,037