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, 2024	Mar. 31, 2023
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-based compensation expense	$ 3,589	$ 3,044
Eastern Bankshares, Inc. 2021 Equity Incentive Plan
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-based compensation expense	3,600	3,000
Related tax benefit	$ 1,000	$ 800