Loans and Allowance for Credit Losses for Loans - Loan Portfolio (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 32,606,814	$ 32,217,112
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	5,635,260	6,861,708
Loans, deferred income, PPP	27,600	43,200
Commercial and industrial | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	4,761,227	4,709,569
Commercial and industrial | Commercial and industrial PPP loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	874,033	2,152,139
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	19,716,650	18,470,823
Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	17,912,070	16,724,998
Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,804,580	1,745,825
Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	4,332,422	4,183,743
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,922,482	2,700,838
Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	402,658	431,553
Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,563,698	1,355,955
Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 956,126	$ 913,330