Loans and Allowance for Credit Losses for Loans - Summary of Collateral Dependent Loans (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
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
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
Collateral Pledged
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	176,027
Collateral Pledged | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	106,239
Collateral Pledged | Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	41,562
Collateral Pledged | Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	28,176
Collateral Pledged | Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 50