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DISCONTINUED OPERATIONS (Details)					1 Months Ended			3 Months Ended			12 Months Ended
DISCONTINUED OPERATIONS (Details)	Jun. 17, 2020 USD ($)	Jun. 11, 2020 USD ($)	Dec. 04, 2019 USD ($)	Jun. 21, 2019 USD ($)	Feb. 29, 2016 defendant	Jan. 31, 2016 USD ($)	Dec. 31, 2013 USD ($) network_lender claim	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) loan	Jul. 24, 2020 Rate	Jul. 21, 2019 USD ($)	May 31, 2017 Rate	Jun. 06, 2012 USD ($)
DISCONTINUED OPERATIONS
Assets								$ 1,188,990,000			$ 1,188,990,000	$ 947,969,000
Damages sought							$ 61,000,000.0
2022 Convertible Notes
DISCONTINUED OPERATIONS
Interest rate								0.625%			0.625%					0.625%
2025 Convertible Notes
DISCONTINUED OPERATIONS
Interest rate								0.50%			0.50%			0.50%
Discover Bank \| Lending Tree Loans
DISCONTINUED OPERATIONS
Asset purchase agreement, proceeds from sale																	$ 55,900,000
Disposed of by means other than sale \| Home Loan Center, Inc.
DISCONTINUED OPERATIONS
Loss from discontinued operations												5,500,000
Gain on disposal											$ 0	4,515,000	$ 0
Recognition of a liability												$ 10,000,000.0
Disposed of by means other than sale \| Loan loss obligations \| Lending Tree Loans
DISCONTINUED OPERATIONS
Settlement payment									$ 36,000,000.0
Home Loan Center, Inc.
DISCONTINUED OPERATIONS
Assets															$ 11,200,000
Cash															$ 5,900,000
Dividends						$ 40,000,000.0
Pending Litigation \| Disposed of by means other than sale \| Loan loss obligations \| Discontinued operations \| Lending Tree Loans
DISCONTINUED OPERATIONS
Amount awarded to other party										$ 36,000,000.0
Residential Funding Co. v Home Loan Center \| Pending Litigation
DISCONTINUED OPERATIONS
Number of loan originators \| network_lender							80
Number of pending claims \| claim							2
Residential Funding Co. v Home Loan Center \| Judicial Ruling
DISCONTINUED OPERATIONS
Amount awarded to other party				$ 68,500,000
Residential Funding Co. v Home Loan Center \| Judicial Ruling \| Damages
DISCONTINUED OPERATIONS
Amount awarded to other party				28,700,000
Residential Funding Co. v Home Loan Center \| Judicial Ruling \| Pre-Verdict Interest
DISCONTINUED OPERATIONS
Amount awarded to other party				14,100,000
Residential Funding Co. v Home Loan Center \| Judicial Ruling \| Attorney Fees
DISCONTINUED OPERATIONS
Amount awarded to other party				23,100,000
Residential Funding Co. v Home Loan Center \| Judicial Ruling \| Pre-Judgment Interest
DISCONTINUED OPERATIONS
Amount awarded to other party				$ 2,600,000
Residential Funding Co. v Home Loan Center \| Settled Litigation \| Damages \| ResCap
DISCONTINUED OPERATIONS
Amount awarded to other party	$ 58,500,000
Settlement payment								$ 6,400,000	26,500,000
Loss contingency receivable								$ 8,600,000			$ 8,600,000
Lehman Brothers Holdings, Inc.
DISCONTINUED OPERATIONS
Amount awarded to other party									$ 500,000
Damages sought			$ 44,700,000										$ 40,200,000
Number of loans sold with losses \| loan													370
Lehman Brothers Holdings, Inc. \| Pending Litigation
DISCONTINUED OPERATIONS
Number of defendants \| defendant					149
Lehman Brothers Holdings Inc. v. LendingTree, LLC
DISCONTINUED OPERATIONS
Damages sought		$ 13,300,000