Loans and Allowance for Credit Losses for Loans - Schedule of Loan Portfolio (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 32,217,112	$ 29,699,208
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	6,861,708	4,825,997
Loans, PPP	2,200,000
Loans, deferred income, PPP	43,200
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	18,470,823	17,643,759
Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	16,724,998	15,996,741
Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,745,825	1,647,018
Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	4,183,743	4,377,111
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,700,838	2,852,341
Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	431,553	487,272
Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,355,955	1,451,623
Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 913,330	$ 913,446