Summary of Significant Accounting Policies - Additional Information (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021 USD ($) segment	Dec. 31, 2020 USD ($)	Mar. 31, 2020 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Unfunded commitments to fund low-income housing partnerships	$ 44,557
Variable interest entity, nonconsolidated, carrying amount, assets	$ 21,947,271	$ 20,603,651	$ 18,542,233
Number of portfolio segments of loans and leases (commercial and consumer) | segment	2
AIR allowance	$ 2,400	2,700
ASU No. 2019-12
Summary Of Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Dec. 15, 2020
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true
Other Liabilities
Summary Of Significant Accounting Policies [Line Items]
Unfunded commitments to fund low-income housing partnerships	$ 44,600	53,000
Low-income Housing Partnerships
Summary Of Significant Accounting Policies [Line Items]
Period over which Federal tax credits or benefits are generally recognized (in years)	10 years
Period over which State tax credits or benefits are generally recognized (in years)	5 years
Solar Energy Partnerships
Summary Of Significant Accounting Policies [Line Items]
Period over which Federal tax credits or benefits are generally recognized (in years)	6 years
Variable Interest Entity Nonconsolidated | Other Assets
Summary Of Significant Accounting Policies [Line Items]
Variable interest entity, nonconsolidated, carrying amount, assets	$ 138,400	$ 143,000