Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total		Cumulative effect accounting adjustment	[1]	Common Stock	Additional Paid in Capital	Retained Earnings	Retained Earnings Cumulative effect accounting adjustment	[1]	Accumulated Other Comprehensive Income	Unallocated Common Stock Held by ESOP
Beginning balance (in shares) at Dec. 31, 2018					0
Beginning balance at Dec. 31, 2018	$ 1,433,141				$ 0	$ 0	$ 1,508,902			$ (75,761)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	135,098						135,098
Other comprehensive income, net of tax	31,914									31,914
Ending balance (in shares) at Dec. 31, 2019					0
Ending balance at Dec. 31, 2019	1,600,153		$ (1,131)		$ 0	0	1,644,000	$ (1,131)		(43,847)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	22,738						22,738
Other comprehensive income, net of tax	98,081									98,081
Proceeds of stock offering and issuance of common shares (net of costs of $28.9 million) (in shares)					179,287,828
Proceeds of stock offering and issuance of common shares (net of costs of $28.9 million)	$ 1,763,980				$ 1,793	1,762,187
Issuance of common shares to the Eastern Bank Foundation (in shares)	7,470,326	[2]			7,470,326
Issuance of common shares donated to the Eastern Bank Foundation	$ 91,287	[2]			$ 75	91,212
Purchase of common shares by the ESOP (in shares)	14,940,652
Purchase of common shares by the ESOP	$ (149,407)										(149,407)
ESOP shares committed to be released	$ 2,351					669					1,682
Ending balance (in shares) at Dec. 31, 2020	186,758,154				186,758,154
Ending balance at Dec. 31, 2020	$ 3,428,052				$ 1,868	1,854,068	1,665,607			54,234	(147,725)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible Enumeration]	Accounting Standards Update 2016-02 [Member]
Dividends to common shareholders	$ (51,619)						(51,619)
Repurchased common stock (in shares)					(1,135,878)
Repurchased common stock	(23,224)				$ (12)	(23,212)
Issuance of restricted stock awards (in shares)					683,056
Issuance of restricted stock awards	0				$ 7	(7)
Net income	154,665						154,665
Other comprehensive income, net of tax	(110,930)									(110,930)
ESOP shares committed to be released	$ 9,408					4,392					5,016
Ending balance (in shares) at Dec. 31, 2021	186,305,332				186,305,332
Ending balance at Dec. 31, 2021	$ 3,406,352				$ 1,863	$ 1,835,241	$ 1,768,653			$ (56,696)	$ (142,709)

[1] Represents cumulative impact on retained earnings pursuant to the Company’s adoption of Accounting Standards Update 2016-02 Leases. The transition adjustment to the opening balance of retained earnings on January 1, 2020 amounted to $1.1 million, net of tax, related to an incremental accrued rent adjustment calculated as a result of electing the hindsight practical expedient.

[2] 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.