Parent Company Only Financial Information - Statement of Cash Flow (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Cash flows from operating activities:
Net income	$ 50,302	$ 42,149	$ 9,825
Adjustments to reconcile net income to net cash from operating activities:
Changes in accrued expense and other liabilities	(8,874)	(12,527)	22,138
ESOP Expense	3,568	2,800
Stock-based compensation	2,910
NET CASH PROVIDED BY OPERATING ACTIVITIES	60,792	43,188	52,899
Cash flows from investing activities:
Acquisition, net of cash and cash equivalents acquired	(48,120)
NET CASH USED IN INVESTING ACTIVITIES	(519,050)	(546,444)	(831,622)
Cash flows from financing activities:
Net proceeds (costs) from stock offering and issuance of common shares		(225)	417,457
Repurchase of common shares under share repurchase plans	(77,125)
Dividends declared and paid	(5,575)
NET CASH PROVIDED BY FINANCING ACTIVITIES	501,999	594,520	894,769
NET CHANGE IN CASH AND CASH EQUIVALENTS	43,741	91,264	116,046
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	363,855	272,591	156,545
CASH AND CASH EQUIVALENTS AT END OF PERIOD	407,596	363,855	272,591
Supplemental disclosure of non-cash transactions:
Restricted stock awards granted	13
Fair value of assets acquired in Provident Acquisition, net of cash	1,320,001
Fair value of liabilities assumed in Provident Acquisition	1,175,739
Goodwill from Provident Acquisition	18,512
Common stock issued for Provident Acquisition	114,654
Parent
Cash flows from operating activities:
Net income	50,302	42,149	9,825
Adjustments to reconcile net income to net cash from operating activities:
Changes in other assets	8,207	(8,670)
Changes in accrued expense and other liabilities	(860)	(26,206)	26,206
ESOP Expense	3,568	2,800
Stock-based compensation	2,910
Equity in undistributed net loss (income) of subsidiary	43,905	(34,403)	(23,386)
NET CASH PROVIDED BY OPERATING ACTIVITIES	108,032	(24,330)	12,645
Cash flows from investing activities:
ESOP share purchases		(33,397)	(13,774)
Investment in Needham Bank			(208,643)
Acquisition, net of cash and cash equivalents acquired	(95,812)
NET CASH USED IN INVESTING ACTIVITIES	(95,812)	(33,397)	(222,417)
Cash flows from financing activities:
Net proceeds (costs) from stock offering and issuance of common shares		(226)	417,457
Repurchase of common shares under share repurchase plans	(77,125)
Dividends declared and paid	(5,575)
NET CASH PROVIDED BY FINANCING ACTIVITIES	(82,700)	(226)	417,457
NET CHANGE IN CASH AND CASH EQUIVALENTS	(70,480)	(57,953)	207,685
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	149,732	207,685
CASH AND CASH EQUIVALENTS AT END OF PERIOD	79,252	$ 149,732	$ 207,685
Supplemental disclosure of non-cash transactions:
Restricted stock awards granted	13
Fair value of assets acquired in Provident Acquisition, net of cash	1,402,027
Fair value of liabilities assumed in Provident Acquisition	1,190,731
Goodwill from Provident Acquisition	18,512
Common stock issued for Provident Acquisition	$ 114,654