Income Taxes - Narrative (Details) - USD ($)		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Examination [Line Items]
Income tax expense		$ 34,047,000	$ 13,163,000	$ 39,481,000
Effective income tax rates		18.04%	36.67%	22.61%
Valuation allowance, deferred tax asset, increase (decrease), amount		$ (11,300,000)
Deferred tax asset valuation allowance		700,000	$ 12,000,000
Issuance of common shares donated to the Eastern Bank Foundation	[1]		91,287,000
Charitable cash contribution			3,700,000
Total deferred tax assets		76,535,000	13,229,000
Unrecognized tax benefits, inclusive of accrued interest and penalties		8,200,000
Unrecognized tax benefits		7,923,000	0
Unrecognized tax benefits that would impact effective tax rate		8,200,000
Unrecognized tax benefits, income tax penalties and interest accrued		2,000,000	0
Unrecognized tax benefits, income tax penalties and interest expense		100,000
Decrease in unrecognized tax benefits is reasonably possible		2,100,000
Decrease in tax interest and penalties is reasonably possible		600,000
Net operating loss carryforwards		0	0
Federal pre-1988 reserve with no tax provision		20,800,000
Tax credits and other tax benefits recognized		6,484,000	5,033,000	$ 5,962,000
Goodwill
Income Tax Examination [Line Items]
Unrecognized tax benefits, income tax penalties and interest accrued		1,900,000
Federal
Income Tax Examination [Line Items]
Tax credits and other tax benefits recognized		6,500,000	7,100,000
State
Income Tax Examination [Line Items]
Tax credits and other tax benefits recognized		$ 0	$ 300,000

[1] Represents a non-cash common stock donation of 7,470,326 shares at a fair value of $91.3 million to the Eastern Bank Foundation. The donation is included in charitable contributions as a non-interest expense in the Consolidated Income Statement for the year ended December 31, 2020.