INCOME TAXES - Carryforwards (Details) - USD ($)		1 Months Ended	12 Months Ended
	Aug. 14, 2019	Jun. 30, 2016	Dec. 31, 2017	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Loss Carryforwards [Line Items]
Net deferred tax asset balance			$ 843,000	$ 9,557,000	$ 6,034,000	$ 6,727,000
Charitable contribution and other carryforwards					15,000
Shares issued	31,036,812
Temporary difference adjustment						320,000
Charitable contribution carryforward expected to be used					1,100,000
Request tax refunds			$ 3,200,000
Federal
Operating Loss Carryforwards [Line Items]
Charitable contribution and other carryforwards						1,100,000
Federal | Tax Year 2013
Operating Loss Carryforwards [Line Items]
Tax refund					(603,000)
Federal | Tax Year 2014
Operating Loss Carryforwards [Line Items]
Tax refund						(826,000)
Federal | Tax Year 2015
Operating Loss Carryforwards [Line Items]
Tax refund						$ (1,300,000)
State | Tax Year 2013
Operating Loss Carryforwards [Line Items]
Tax refund					(211,000)
State | Tax Year 2014
Operating Loss Carryforwards [Line Items]
Tax refund					(320,000)
State | Tax Year 2015
Operating Loss Carryforwards [Line Items]
Tax refund					$ (40,000)
HarborOne Foundation
Operating Loss Carryforwards [Line Items]
Shares issued		385,450
Cash		$ 965,000
HarborOne Bank | Maximum
Operating Loss Carryforwards [Line Items]
Net operating loss that can be used per year				552,000
HarborOne Bank | New Hampshire | HarborOne Mortgage
Operating Loss Carryforwards [Line Items]
Net operating loss				1,700,000
Net deferred tax asset balance				$ 10,000