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Retirement Benefit Plans - Narrative (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Jul. 01, 2024
Defined Benefit Plan Disclosure [Line Items]
Expected long-term rate of return	6.00%
Shortfall amortization period	15 years
Funded status of plan				$ 3.3
Sterling National Bank 401k And Profit Sharing Plan
Defined Benefit Plan Disclosure [Line Items]
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%
Compensation expense	$ 20.6	$ 20.3	$ 18.2
Webster Bank Retirement Savings Plan
Defined Benefit Plan Disclosure [Line Items]
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%
Fixed Income Funds
Defined Benefit Plan Disclosure [Line Items]
Actual asset allocation percentages	64.10%
Target asset allocation percentage	64.50%
Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Actual asset allocation percentages	35.30%
Target asset allocation percentage	35.50%
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Actual asset allocation percentages	0.60%

X

- Definition

Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
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-Name Accounting Standards Codification
-Section 50
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-URI https://asc.fasb.org/1943274/2147480506/715-20-50-8

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Amount of funded (unfunded) status of defined benefit plan, measured as difference between fair value of plan assets and benefit obligation. Includes, but is not limited to, overfunded (underfunded) status.

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Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

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Amount of cost for defined contribution plan.

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Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

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