Loans Composition (Details) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Loans and Leases Receivable Disclosure [Line Items]
Total loans(a)(b)	$ 22,754,710	$ 22,940,429
Commercial and industrial
Loans and Leases Receivable Disclosure [Line Items]
Total loans(a)(b)	7,495,623	7,398,044
Commercial real estate — owner occupied
Loans and Leases Receivable Disclosure [Line Items]
Total loans(a)(b)	915,524	920,443
Commercial and business lending
Loans and Leases Receivable Disclosure [Line Items]
Total loans(a)(b)	8,411,147	8,318,487
Commercial real estate — investor
Loans and Leases Receivable Disclosure [Line Items]
Total loans(a)(b)	3,803,277	3,751,554
Real estate construction
Loans and Leases Receivable Disclosure [Line Items]
Total loans(a)(b)	1,356,508	1,335,031
Commercial real estate lending
Loans and Leases Receivable Disclosure [Line Items]
Total loans(a)(b)	5,159,784	5,086,585
Total commercial
Loans and Leases Receivable Disclosure [Line Items]
Total loans(a)(b)	13,570,932	13,405,072
Residential mortgage
Loans and Leases Receivable Disclosure [Line Items]
Total loans(a)(b)	$ 7,954,801	8,277,712
Approximate Carrying Amount of Loans Sold	approximately $240 million
Home equity
Loans and Leases Receivable Disclosure [Line Items]
Total loans(a)(b)	$ 879,642	894,473
Other consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans(a)(b)	349,335	363,171
Total consumer
Loans and Leases Receivable Disclosure [Line Items]
Total loans(a)(b)	9,183,778	9,535,357
Carrying Amount Of Loans Sold	33,000
Bank Mutual
Loans and Leases Receivable Disclosure [Line Items]
Purchased credit-impaired loans	$ 2,000	$ 5,000