Loans, Loan Composition (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income	$ 22,940,429	$ 20,784,991
Commercial and industrial
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income	7,398,044	6,399,693
Commercial real estate - owner occupied
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income	920,443	802,209
Commercial and business lending
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income	8,318,487	7,201,902
Commercial real estate — investor
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income	3,751,554	3,315,254
Real estate construction
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income	1,335,031	1,451,684
Commercial real estate lending
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income	5,086,585	4,766,938
Total commercial
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income	13,405,072	11,968,840
Residential mortgage
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income	8,277,712	7,546,534
Home equity
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income	894,473	883,804
Other consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income	363,171	385,813
Total consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income	9,535,357	$ 8,816,151
Bank Mutual [Member]
Loans and Leases Receivable Disclosure [Line Items]
Purchased credit-impaired loans	$ 5,000