Loans, Loan Composition (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Loans and Leases Receivable Disclosure [Line Items]
Total loans	$ 19,844,005	$ 18,714,343
Commercial and industrial
Loans and Leases Receivable Disclosure [Line Items]
Total loans	6,721,557	6,190,683
Commercial real estate — owner occupied
Loans and Leases Receivable Disclosure [Line Items]
Total loans	892,678	918,212
Commercial and business lending
Loans and Leases Receivable Disclosure [Line Items]
Total loans	7,614,235	7,108,895
Commercial real estate — investor
Loans and Leases Receivable Disclosure [Line Items]
Total loans	3,530,370	3,234,266
Real estate construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans	1,314,431	1,162,145
Commercial real estate lending
Loans and Leases Receivable Disclosure [Line Items]
Total loans	4,844,801	4,396,411
Total commercial
Loans and Leases Receivable Disclosure [Line Items]
Total loans	12,459,036	11,505,306
Residential mortgage
Loans and Leases Receivable Disclosure [Line Items]
Total loans	6,034,166	5,783,267
Home equity
Loans and Leases Receivable Disclosure [Line Items]
Total loans	951,594	1,005,802
Other consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans	399,209	419,968
Total consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans	$ 7,384,969	$ 7,209,037