Loans and Allowance for Credit Losses for Loans - Summary of Collateral Dependent Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 32,686,416	$ 32,217,112
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	7,148,644	6,861,708
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	18,709,958	18,470,823
Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	16,923,627	16,724,998
Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	4,060,492	4,183,743
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,767,322	2,700,838
Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	409,576	431,553
Collateral Pledged
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	203,009	176,027
Collateral Pledged | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	110,169	106,239
Collateral Pledged | Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	60,647	41,562
Collateral Pledged | Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	32,144	28,176
Collateral Pledged | Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 49	$ 50