Loans, Loan Composition (Details) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income		$ 22,821,440	$ 22,940,429
Commercial and industrial
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income		7,354,594	7,398,044
Commercial real estate - owner occupied
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income		911,265	920,443
Commercial and business lending
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income		8,265,858	8,318,487
Commercial real estate - investor
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income		3,794,517	3,751,554
Real estate construction
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income		1,420,900	1,335,031
Commercial real estate lending
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income		5,215,417	5,086,585
Total commercial
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income		13,481,275	13,405,072
Residential mortgage
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income		8,136,980	8,277,712
Approximate Carrying Amount of Loans Sold	approximately $240 million
Home equity
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income		852,025	894,473
Other consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income		351,159	363,171
Total consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Net of Deferred Income		9,340,164	9,535,357
Carrying Amount Of Loans Sold	$ 33,000
Bank Mutual [Member]
Loans and Leases Receivable Disclosure [Line Items]
Purchased credit-impaired loans		$ 2,000	$ 5,000