MINIMUM REGULATORY CAPITAL REQUIREMENTS (Details)	12 Months Ended
	Dec. 31, 2023 USD ($) $ / shares shares	Dec. 31, 2022 USD ($) $ / shares shares	Dec. 31, 2021 USD ($) $ / shares shares	Sep. 21, 2022 shares
Compliance with Regulatory Capital Requirements under Banking Regulations
Common equity Tier 1 capital conversation buffer ratio	0.025
Applicable capital conversation buffer ratio	0.025
Number of previous years net income is retained	2 years
Common equity Tier 1 to risk-weighted assets
Actual, Capital amount	$ 567,248,000	$ 592,610,000
Actual, Ratio	0.120	0.128
Minimum Requirement for Capital Adequacy Purposes	$ 212,816,000	$ 208,541,000
Minimum Requirement for Capital Adequacy Purposes, ratio	0.045	0.045
Tier 1 capital to risk weighted assets
Actual, Capital amount	$ 567,248,000	$ 592,610,000
Actual, Ratio	0.120	0.128
Minimum Requirement for Capital Adequacy Purposes	$ 283,755,000	$ 278,054,000
Minimum Requirement for Capital Adequacy Purposes, ratio	0.060	0.060
Total capital to risk-weighted assets
Actual, Capital amount	$ 619,138,000	$ 677,774,000
Actual, Ratio	0.131	0.146
Minimum Requirement for Capital Adequacy Purposes	$ 378,340,000	$ 370,739,000
Minimum Requirement for Capital Adequacy Purposes, ratio	0.080	0.080
Tier 1 capital to average assets
Actual, Capital amount	$ 567,248,000	$ 592,610,000
Actual, Ratio	0.100	0.115
Minimum Requirement for Capital Adequacy Purposes	$ 226,690,000	$ 205,897,000
Minimum Requirement for Capital Adequacy Purposes, ratio	0.040	0.040
Preferred Stock
Preferred stock, shares authorized | shares	1,000,000	1,000,000
Preferred Stock, Par Value Per Share | $ / shares	$ 0	$ 0
Preferred Stock, shares issued | shares	0	0
Preferred Stock, shares outstanding | shares	0	0
Treasury Stock
Shares available for repurchase | shares				2,325,489
Treasury stock, additional shares acquired related to tax obligations | shares	25,439	67,934	42,925
Treasury stock additional shares acquired associated with tax obligations, average cost per share | $ / shares	$ 13.42	$ 14.44	$ 14.27
Treasury stock, additional shares acquired related to tax obligations, value	$ 341,000	$ 981,000	$ 613,000
Total treasury stock	$ 45,206,000	$ 62,525,000	$ 69,215,000
Share Repurchase Programs
Treasury Stock
Shares acquired, average cost per share | $ / shares	$ 12.03	$ 14.16	$ 13.68
Total treasury stock	$ 44,900,000	$ 61,500,000	$ 68,600,000
Treasury Stock purchased (in shares) | shares	3,728,550	4,338,637	5,021,067
HarborOne Bank.
Common equity Tier 1 to risk-weighted assets
Actual, Capital amount	$ 509,791,000	$ 525,522,000
Actual, Ratio	0.108	0.113
Minimum Requirement for Capital Adequacy Purposes	$ 212,724,000	$ 208,447,000
Minimum Requirement for Capital Adequacy Purposes, ratio	0.045	0.045
Minimum Required to be Considered "Well Capitalized" Under Prompt Corrective Action Provisions	$ 307,267,000	$ 301,090,000
Minimum Required to be Considered "Well Capitalized" Under Prompt Corrective Action Provisions, ratio	0.065	0.065
Tier 1 capital to risk weighted assets
Actual, Capital amount	$ 509,791,000	$ 525,522,000
Actual, Ratio	0.108	0.113
Minimum Requirement for Capital Adequacy Purposes	$ 283,632,000	$ 277,929,000
Minimum Requirement for Capital Adequacy Purposes, ratio	0.060	0.060
Minimum Required to be Considered "Well Capitalized" Under Prompt Corrective Action Provisions	$ 378,175,000	$ 370,572,000
Minimum Required to be Considered "Well Capitalized" Under Prompt Corrective Action Provisions, ratio	0.080	0.080
Total capital to risk-weighted assets
Actual, Capital amount	$ 561,682,000	$ 575,686,000
Actual, Ratio	0.119	0.124
Minimum Requirement for Capital Adequacy Purposes	$ 378,175,000	$ 370,572,000
Minimum Requirement for Capital Adequacy Purposes, ratio	0.080	0.080
Minimum Required to be Considered "Well Capitalized" Under Prompt Corrective Action Provisions	$ 472,719,000	$ 463,215,000
Minimum Required to be Considered "Well Capitalized" Under Prompt Corrective Action Provisions, ratio	0.100	0.100
Tier 1 capital to average assets
Actual, Capital amount	$ 509,791,000	$ 525,522,000
Actual, Ratio	0.090	0.102
Minimum Requirement for Capital Adequacy Purposes	$ 226,666,000	$ 205,874,000
Minimum Requirement for Capital Adequacy Purposes, ratio	0.040	0.040
Minimum Required to be Considered "Well Capitalized" Under Prompt Corrective Action Provisions	$ 283,333,000	$ 257,342,000
Minimum Required to be Considered "Well Capitalized" Under Prompt Corrective Action Provisions, ratio	0.050	0.050