Commitments and Contingencies - Summary of Financial Instruments with Off-Balance Sheet Risk (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance sheet risk	$ 7,845,683	$ 7,575,781
Standby letters of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance sheet risk	293,900	296,036
Commitments to sell loans
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance sheet risk	155,627	68,492
Commercial letters of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Commercial letters of credit	1,663	2,887
Commitments under commercial loans and lines of credit | Commitments under commercial loans and lines of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance sheet risk	5,595,561	5,550,967
Home equity and other revolving lines of credit | Unused lines of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance sheet risk	1,485,911	1,379,581
Outstanding residential mortgage loan commitments | Outstanding residential mortgage loan commitments
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance sheet risk	244,286	233,291
Commitments under unused lines of credit—credit card | Unused lines of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance sheet risk	$ 68,735	$ 44,527