Consolidated Statements of Cash Flows - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating activities
Net income		$ 154,665	$ 22,738	$ 135,098
Adjustments to reconcile net income to net cash provided by operating activities
(Release of) provision for loan losses		(9,686)	38,800	6,300
Depreciation and amortization		14,479	15,827	19,482
(Accretion) amortization of deferred loan fees and premiums, net		(27,991)	(14,574)	5,130
Deferred income tax (benefit) expense		(5,313)	(20,359)	1,376
Amortization of investment security premiums and discounts, net		16,713	5,585	3,063
Right-of-use asset amortization		12,703	12,082	0
Increase in cash surrender value of bank-owned life insurance		(2,348)	(2,188)	(2,112)
Gain on life insurance benefits		(1,813)	(174)	0
Gain on sale of securities available for sale, net		(1,166)	(288)	(2,016)
Loss on bank premises and equipment, net		4,715	73	271
Loss on lease termination/modification, net		2,182	0	0
Amortization of gains from terminated interest rate swaps		(31,234)	(15,889)	0
ESOP expense		9,408	2,351	0
Issuance of common shares donated to the Eastern Bank Foundation		0	91,287	0
Other		(526)	(587)	0
Change in:
Trading securities		0	961	51,938
Loans held for sale		(47)	(1,133)	(4)
Prepaid pension expense		1,130	(24,055)	(11,031)
Other assets		61,501	(89,590)	(30,952)
Other liabilities		(22,882)	48,984	19,680
Net cash provided by operating activities		174,490	69,851	196,223
Investing activities
Proceeds from sales of securities available for sale		23,798	9,097	47,985
Proceeds from maturities and principal paydowns of securities available for sale		939,575	452,392	204,065
Purchases of securities available for sale		(3,323,893)	(2,111,773)	(252,571)
Proceeds from sale of Federal Home Loan Bank stock		6,692	749	42,034
Purchases of Federal Home Loan Bank stock		(2,101)	(527)	(33,102)
Contributions to low income housing tax credit investments		(11,379)	(12,372)	(6,349)
Contributions to other equity investments		(2,519)	(4,395)	(4,545)
Distributions from other equity investments		337	201	62
Proceeds from life insurance policies		0	1,347	0
Net decrease (increase) in outstanding loans		380,807	(719,041)	(135,666)
Acquisitions, net of cash and cash equivalents acquired		(13,439)	(1,363)	0
Purchased banking premises and equipment, net		(5,728)	(5,144)	(7,187)
Proceeds from sale of premises held for sale		21,981	0	0
Proceeds from sale of other real estate owned		125	646	0
Net cash used in investing activities		(1,985,744)	(2,390,183)	(145,274)
Financing activities
Net increase in demand, savings, interest checking, and money market investment deposit accounts	[1]	1,155,868	2,674,672	297,708
Net decrease in time deposits		(58,144)	(70,280)	(145,809)
Net increase (decrease) in borrowed funds		2,580	(207,346)	(98,892)
Repayments of acquired subordinated debentures	[2]	(36,277)	0	0
Contingent consideration paid		(263)	(165)	(716)
Proceeds from issuance of common shares		0	1,792,878	0
Purchase of shares by the ESOP		0	(149,407)	0
Payment of deferred offering costs		0	(28,552)	(346)
Payments for repurchases of common stock		(23,224)	0	0
Dividends declared and paid to common shareholders		(51,564)	0	0
Net cash provided by financing activities		988,976	4,011,800	51,945
Net (decrease) increase in cash, cash equivalents, and restricted cash		(822,278)	1,691,468	102,894
Cash, cash equivalents, and restricted cash at beginning of period		2,054,070	362,602	259,708
Cash, cash equivalents, and restricted cash at end of period		1,231,792	2,054,070	362,602
Supplemental disclosure of cash flow information
Interest paid		5,354	13,684	34,217
Income taxes		43,299	35,128	31,308
Non-cash activities
Net increase in capital commitments relating to low income housing tax credit projects		28,291	25,816	10,000
Maturity of acquired securities sold under agreements to repurchase	[1]	274,982	0	0
Initial recognition of operating lease right-of-use assets upon adoption of ASU 2016-02		0	92,948	0
Initial recognition of operating lease liabilities upon adoption of ASU 2016-02		$ 0	$ 96,426	$ 0

[1] Includes non-cash item representing maturity of acquired securities sold under agreements to repurchase which were converted to deposits upon maturity.

[2] The Company deposited funds into escrow prior to the Century acquisition date to pay the balance of subordinated debentures assumed in the Century acquisition which was considered to be a defeasance of the debt. Accordingly, Century recorded a payable to the Company in the amount of the escrow deposit and the Company recorded a receivable from Century in the same amount. The payable was reclassified to other assets upon acquisition and is reflected as such balance in the summary of net assets acquired included in Note 3 to the consolidated financial statements. Subsequent to the closing of the acquisition and prior to December 31, 2021, the amounts placed in escrow were disbursed to the holders of the subordinated debentures resulting in a full pay-off of the outstanding balance of the debt.