Loans and Allowance for Credit Losses for Loans - Summary of Collateral Dependent Loans (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 32,457,454	$ 32,217,112
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	6,084,455	6,861,708
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	19,264,980	18,470,823
Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	17,512,142	16,724,998
Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	4,226,975	4,183,743
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,881,044	2,700,838
Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	410,856	431,553
Collateral Pledged
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	192,816	176,027
Collateral Pledged | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	95,000	106,239
Collateral Pledged | Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	66,054	41,562
Collateral Pledged | Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	31,714	28,176
Collateral Pledged | Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 48	$ 50