MINIMUM REGULATORY CAPITAL REQUIREMENTS (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2022 USD ($)	Dec. 31, 2021 USD ($)
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
Common equity Tier 1 to risk-weighted assets
Actual, Capital amount	$ 586,990	$ 608,804
Actual, Ratio	0.145	0.164
Minimum Requirement for Capital Adequacy Purposes	$ 182,699	$ 167,475
Minimum Requirement for Capital Adequacy Purposes, ratio	0.045	0.045
Tier 1 capital to risk weighted assets
Actual, Capital amount	$ 586,990	$ 608,804
Actual, Ratio	0.145	0.164
Minimum Requirement for Capital Adequacy Purposes	$ 243,599	$ 223,300
Minimum Requirement for Capital Adequacy Purposes, ratio	0.060	0.060
Total capital to risk-weighted assets
Actual, Capital amount	$ 670,646	$ 689,181
Actual, Ratio	0.165	0.185
Minimum Requirement for Capital Adequacy Purposes	$ 324,799	$ 297,733
Minimum Requirement for Capital Adequacy Purposes, ratio	0.080	0.080
Tier 1 capital to average assets
Actual, Capital amount	$ 586,990	$ 608,804
Actual, Ratio	0.128	0.136
Minimum Requirement for Capital Adequacy Purposes	$ 182,828	$ 179,710
Minimum Requirement for Capital Adequacy Purposes, ratio	0.040	0.040
HarborOne Bank.
Common equity Tier 1 to risk-weighted assets
Actual, Capital amount	$ 504,759	$ 485,239
Actual, Ratio	0.124	0.131
Minimum Requirement for Capital Adequacy Purposes	$ 182,682	$ 166,660
Minimum Requirement for Capital Adequacy Purposes, ratio	0.045	0.045
Minimum Required to be Considered "Well Capitalized" Under Prompt Corrective Action Provisions	$ 263,874	$ 240,731
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	$ 504,759	$ 485,239
Actual, Ratio	0.124	0.131
Minimum Requirement for Capital Adequacy Purposes	$ 243,576	$ 222,214
Minimum Requirement for Capital Adequacy Purposes, ratio	0.060	0.060
Minimum Required to be Considered "Well Capitalized" Under Prompt Corrective Action Provisions	$ 324,768	$ 296,285
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	$ 553,415	$ 530,616
Actual, Ratio	0.136	0.143
Minimum Requirement for Capital Adequacy Purposes	$ 324,768	$ 296,285
Minimum Requirement for Capital Adequacy Purposes, ratio	0.080	0.080
Minimum Required to be Considered "Well Capitalized" Under Prompt Corrective Action Provisions	$ 405,960	$ 370,356
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	$ 504,759	$ 485,239
Actual, Ratio	0.110	0.109
Minimum Requirement for Capital Adequacy Purposes	$ 182,792	$ 178,279
Minimum Requirement for Capital Adequacy Purposes, ratio	0.040	0.040
Minimum Required to be Considered "Well Capitalized" Under Prompt Corrective Action Provisions	$ 228,491	$ 222,849
Minimum Required to be Considered "Well Capitalized" Under Prompt Corrective Action Provisions, ratio	0.050	0.050