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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% |  |  |

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- 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 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 8 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-8 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (k)(3) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480535/715-20-45-2 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(i) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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- Definition Percentage of actual investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(i) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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- Definition Amount of cost for defined contribution plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 70 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480794/715-70-50-1 + Details
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- Definition Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan. + References No definition available. + Details
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