Employee Benefits - Schedule of Share-based Compensation Expense Under the 2021 Plan and the Related Tax Benefit (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2026	Mar. 31, 2025
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-based compensation expense	$ 4,158	$ 4,752
Eastern Bankshares, Inc. 2021 Equity Incentive Plan
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-based compensation expense	4,200	4,800
Related tax benefit	$ 1,200	$ 1,300

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.

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+ Details