Retirement Benefit Plans - Narrative (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Jul. 01, 2021
Defined Benefit Plan Disclosure [Line Items]
Expected Long-Term Rate of Return on Plan Assets	5.50%
Shortfall amortization period	7 years
Funded status of plan				$ 2.1
Sterling National Bank 401k And Profit Sharing Plan
Defined Benefit Plan Disclosure [Line Items]
Employee annual contribution percent of eligible compensation	50.00%
Employer matching contribution, percent of match	50.00%
Maximum employee contributions of eligible compensation	4.00%
Maximum match	2.00%
Profit sharing contribution	3.00%
Salary deferral contributions automatic increase	1.00%
Salary maximum deferral contributions automatic increase	10.00%
Compensation expense	$ 18.2	$ 13.1	$ 13.8
Webster Bank Retirement Savings Plan
Defined Benefit Plan Disclosure [Line Items]
Employee annual contribution percent of eligible compensation	75.00%
Employer matching contribution, percent of match	100.00%
Employer matching contribution, percent of employees' gross pay	2.00%
Employer matching contribution, additional percent of match	50.00%
Employer additional matching contribution, percent of employees' gross pay	6.00%
Employer additional matching contribution, percent of employees' gross pay, default	3.00%
Fixed Income Funds
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation percentage	64.50%
Actual asset allocation percentages	63.80%
Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation percentage	35.50%
Actual asset allocation percentages	35.40%
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Actual asset allocation percentages	0.80%