SEGMENT REPORTING (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2022 USD ($) segment	Sep. 30, 2021 USD ($)	Dec. 31, 2021 USD ($)
Segment Reporting Information
Number of reportable segments | segment			2
Net interest and dividend income (expense)	$ 39,332	$ 32,803	$ 109,797	$ 97,385
Provision (benefit) for credit losses	668	(1,627)	3,552	(5,822)
Net interest and dividend income, after provision (benefit) for credit losses	38,664	34,430	106,245	103,207
Mortgage banking income:
Gain on sale of mortgage loans	3,809	12,756	13,669	51,820
Changes in mortgage servicing rights fair value	1,816	(992)	7,963	(135)
Other	2,453	3,882	7,623	12,472
Total mortgage banking income	8,078	15,646	29,255	64,157
Other noninterest income (loss)	6,167	6,364	18,154	17,365
Total noninterest income	14,245	22,010	47,409	81,522
Noninterest expense	34,473	39,274	104,262	120,674
Income (loss) before income taxes	18,436	17,166	49,392	64,055
Income tax benefit	4,678	4,907	13,380	18,128
Net income	13,758	12,259	36,012	45,927
Total assets at period end	4,987,643	4,567,094	4,987,643	4,567,094	$ 4,553,405
Goodwill at period end	69,802	69,802	69,802	69,802	$ 69,802
HarborOne Bank
Mortgage banking income:
Goodwill at period end	59,000		59,000
HarborOne Mortgage.
Mortgage banking income:
Goodwill at period end	10,800		10,800
Operating Segments | HarborOne Bank
Segment Reporting Information
Net interest and dividend income (expense)	39,373	32,494	110,043	95,876
Provision (benefit) for credit losses	668	(1,627)	3,552	(5,822)
Net interest and dividend income, after provision (benefit) for credit losses	38,705	34,121	106,491	101,698
Mortgage banking income:
Intersegment gain (loss)	(904)	(1,373)	(2,607)	(2,945)
Changes in mortgage servicing rights fair value	164	(74)	881	(207)
Other	218	263	670	839
Total mortgage banking income	(522)	(1,184)	(1,056)	(2,313)
Other noninterest income (loss)	6,180	6,339	18,151	17,328
Total noninterest income	5,658	5,155	17,095	15,015
Noninterest expense	27,707	26,570	81,663	75,161
Income (loss) before income taxes	16,656	12,706	41,923	41,552
Income tax benefit	4,166	3,575	11,273	11,873
Net income	12,490	9,131	30,650	29,679
Total assets at period end	5,000,963	4,575,798	5,000,963	4,575,798
Goodwill at period end	59,042	59,042	59,042	59,042
Operating Segments | HarborOne Mortgage.
Segment Reporting Information
Net interest and dividend income (expense)	437	792	1,198	2,897
Net interest and dividend income, after provision (benefit) for credit losses	437	792	1,198	2,897
Mortgage banking income:
Gain on sale of mortgage loans	3,809	12,756	13,669	51,820
Intersegment gain (loss)	698	2,366	2,632	3,938
Changes in mortgage servicing rights fair value	1,652	(918)	7,082	72
Other	2,235	3,619	6,953	11,633
Total mortgage banking income	8,394	17,823	30,336	67,463
Other noninterest income (loss)	(13)	25	3	37
Total noninterest income	8,381	17,848	30,339	67,500
Noninterest expense	6,610	12,387	21,613	44,545
Income (loss) before income taxes	2,208	6,253	9,924	25,852
Income tax benefit	687	1,559	2,777	6,905
Net income	1,521	4,694	7,147	18,947
Total assets at period end	132,431	208,888	132,431	208,888
Goodwill at period end	$ 10,760	$ 10,760	$ 10,760	$ 10,760