Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 50,302,000	$ 42,149,000	$ 9,825,000
Adjustments to reconcile net income to net cash from operating activities:
Net accretion of available-for-sale securities	(291,000)	(336,000)	(240,000)
Loss on sale of available-for-sale securities, net		1,867,000
Amortization of core deposit intangible	576,000	149,000	149,000
Provision for credit losses	4,653,000	12,123,000	13,885,000
Loan hedge fair value adjustments, including amortization	140,000	130,000	161,000
Change in net deferred loan origination fees	1,337,000	1,386,000	4,419,000
Mortgage loans originated for sale	(6,525,000)	(14,137,000)	(2,400,000)
Proceeds from sale of mortgage loans held for sale	8,860,000	23,934,000	2,405,000
Write down on consumer loans transferred to held for sale	517,000
Gain on sale of mortgage loans	(165,000)	(293,000)	(5,000)
Depreciation and amortization expense	3,022,000	2,815,000	2,678,000
Gain from BOLI death benefit	(25,000)
Increase in cash surrender values of BOLI	(3,268,000)	(2,269,000)	(1,510,000)
Deferred income tax expense (benefit)	3,330,000	(10,255,000)	(7,720,000)
ESOP expense	3,568,000	2,800,000
Stock-based compensation	2,910,000
Changes in operating assets and liabilities:
Accrued interest receivable	(1,144,000)	(2,401,000)	(6,462,000)
Prepaid expenses and other assets	5,123,000	(6,543,000)	8,177,000
Accrued expenses and other liabilities	(8,874,000)	(12,527,000)	22,138,000
Accrued retirement liabilities	(3,254,000)	4,596,000	7,399,000
NET CASH PROVIDED BY OPERATING ACTIVITIES	60,792,000	43,188,000	52,899,000
CASH FLOWS FROM INVESTING ACTIVITIES
Loan originations and purchases, net of repayments	(505,958,000)	(463,928,000)	(882,960,000)
Purchases of available-for-sale securities	(101,500,000)	(142,985,000)	(43,590,000)
Proceeds from sales of available-for-sale securities	23,963,000	27,444,000	0
Proceeds from maturities, calls and paydowns of available-for-sale securities	67,475,000	80,120,000	103,585,000
Recoveries of loans previously charged off	2,264,000	623,000	924,000
Net change in non-public investments	(2,649,000)	4,220,000	(6,716,000)
Acquisition, net of cash and cash equivalents acquired	(48,120,000)
Proceeds from BOLI death benefit	128,000
Proceeds from surrender (purchases) of BOLI policies	48,764,000	(50,000,000)
Purchases of banking premises and equipment	(3,417,000)	(1,938,000)	(2,865,000)
NET CASH USED IN INVESTING ACTIVITIES	(519,050,000)	(546,444,000)	(831,622,000)
CASH FLOWS FROM FINANCING ACTIVITIES
Net change in deposits	540,120,000	790,325,000	500,665,000
Net change in mortgagors' escrow accounts	4,000	320,000	165,000
Net proceeds (costs) from stock offering and issuance of common shares		(225,000)	417,457,000
Purchase of common shares held by ESOP		(33,397,000)	(13,774,000)
Repurchase of common shares under share repurchase plans	(77,125,000)
Dividends declared and paid	(5,575,000)
(Decrease) increase in FHLB borrowings, net	44,575,000	(162,503,000)	(9,744,000)
NET CASH PROVIDED BY FINANCING ACTIVITIES	501,999,000	594,520,000	894,769,000
NET CHANGE IN CASH AND CASH EQUIVALENTS	43,741,000	91,264,000	116,046,000
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	363,855,000	272,591,000	156,545,000
CASH AND CASH EQUIVALENTS AT END OF PERIOD	407,596,000	363,855,000	272,591,000
Supplemental disclosure of cash paid during the period for:
Interest	143,283,000	128,348,000	88,746,000
Supplemental disclosure of non-cash transactions:
Initial recognition of operating lease right of use assets and lease liabilities	2,662,000
Increase in operating lease right of use assets and lease liabilities resulting from lease modifications	2,732,000
Unrealized gains on available-for-sale securities	6,355,000	4,850,000	3,740,000
Unrealized holding losses (gains) on cash flow hedge	1,284,000		(321,000)
Mortgage loans transferred to loans held for sale	2,244,000	9,504,000
Consumer loans transferred to loans held for sale	66,964,000
Unrealized pension losses (gains) from director pension plan	948,000	(262,000)	106,000
Restricted stock awards granted	13,000
Fair value of assets acquired in Provident Acquisition, net of cash	1,320,001,000
Fair value of liabilities assumed in Provident Acquisition	1,175,739,000
Goodwill from Provident Acquisition	18,512,000
Common stock issued for Provident Acquisition	114,654,000
U.S. Federal
Supplemental disclosure of cash paid during the period for:
Income taxes	900,000	5,800,000	704,000
Massachusetts
Supplemental disclosure of cash paid during the period for:
Income taxes	4,425,000	6,500,000	4,080,000
Jurisdictions below 5 percent of total income taxes paid, net of refunds
Supplemental disclosure of cash paid during the period for:
Income taxes	$ 739,000	792,000	7,000
ASU 2016-13
Supplemental disclosure of non-cash transactions:
Cumulative effect adjustment of adoption of ASU, net of income taxes			$ (2,118,000)
ASU 2023-02
Supplemental disclosure of non-cash transactions:
Cumulative effect adjustment of adoption of ASU, net of income taxes		$ 7,849,000