MINIMUM REGULATORY CAPITAL REQUIREMENTS (Details) $ in Thousands	9 Months Ended
	Sep. 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	$ 588,467	$ 608,804
Actual, Ratio	0.134	0.164
Minimum Requirement for Capital Adequacy Purposes	$ 197,880	$ 167,475
Minimum Requirement for Capital Adequacy Purposes, ratio	0.045	0.045
Tier 1 capital to risk weighted assets
Actual, Capital amount	$ 588,467	$ 608,804
Actual, Ratio	0.134	0.164
Minimum Requirement for Capital Adequacy Purposes	$ 263,839	$ 223,300
Minimum Requirement for Capital Adequacy Purposes, ratio	0.060	0.060
Total capital to risk-weighted assets
Actual, Capital amount	$ 673,590	$ 689,181
Actual, Ratio	0.153	0.185
Minimum Requirement for Capital Adequacy Purposes	$ 351,786	$ 297,733
Minimum Requirement for Capital Adequacy Purposes, ratio	0.080	0.080
Tier 1 capital to average assets
Actual, Capital amount	$ 588,467	$ 608,804
Actual, Ratio	0.123	0.136
Minimum Requirement for Capital Adequacy Purposes	$ 191,473	$ 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	$ 517,127	$ 485,239
Actual, Ratio	0.118	0.131
Minimum Requirement for Capital Adequacy Purposes	$ 197,813	$ 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	$ 285,731	$ 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	$ 517,127	$ 485,239
Actual, Ratio	0.118	0.131
Minimum Requirement for Capital Adequacy Purposes	$ 263,751	$ 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	$ 351,668	$ 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	$ 567,251	$ 530,616
Actual, Ratio	0.129	0.143
Minimum Requirement for Capital Adequacy Purposes	$ 351,668	$ 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	$ 439,585	$ 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	$ 517,127	$ 485,239
Actual, Ratio	0.108	0.109
Minimum Requirement for Capital Adequacy Purposes	$ 191,434	$ 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	$ 239,293	$ 222,849
Minimum Required to be Considered "Well Capitalized" Under Prompt Corrective Action Provisions, ratio	0.050	0.050