DISCONTINUED OPERATIONS (Details-Disposal Groups) - USD ($) $ in Thousands		1 Months Ended			3 Months Ended		9 Months Ended		12 Months Ended
	Dec. 04, 2019	Jul. 31, 2020	Jan. 31, 2016	Dec. 31, 2013	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2018	Jul. 24, 2020	Dec. 31, 2019	Jul. 21, 2019	May 31, 2017	Jun. 06, 2012
DISCONTINUED OPERATIONS
Loss Contingency, Damages Sought, Value				$ 61,000
Assets					$ 1,203,589		$ 1,203,589				$ 947,969
Revenue and net income (loss) of discontinued operations
Revenue					0	$ 0	0	$ 0
Other operating gains (expenses)					193	(32,182)	(34,333)	(34,492)
Income (loss) before income taxes					193	(27,667)	(34,333)	(29,977)
Income tax (expense) benefit					(27)	7,468	8,783	7,953
Loss from discontinued operations					166	(20,199)	(25,550)	(22,024)
Assets and liabilities of facilities reported as discontinued operations
Annual interest rate on convertible senior notes										0.50%			0.625%
Lending Tree Loans | Discover
DISCONTINUED OPERATIONS
Asset purchase agreement proceeds from sale														$ 55,900
Home Loan Center, Inc.
DISCONTINUED OPERATIONS
Assets												$ 11,200
Assets and liabilities of facilities reported as discontinued operations
Cash												$ 5,900
Dividends			$ 40,000
Discontinued Operations, Disposed of by Means Other than Sale [Member] | Home Loan Center, Inc.
Revenue and net income (loss) of discontinued operations
Net gain related to removal of HLC					0	4,515	$ 0	$ 4,515
Assets and liabilities of facilities reported as discontinued operations
Loss recognized						5,500
Recognition of liability						$ 10,000
Discontinued Operations, Disposed of by Means Other than Sale [Member] | Obligation to Repurchase Receivables Sold | Lending Tree Loans
DISCONTINUED OPERATIONS
Loss contingency settlement payment		$ 36,000
Pending Settlement | Discontinued Operations, Disposed of by Means Other than Sale [Member] | Discontinued Operations | Obligation to Repurchase Receivables Sold | Lending Tree Loans
DISCONTINUED OPERATIONS
Settlement value of indemnification claim and other miscellaneous items					36,000
Lehman Brothers Holdings, Inc. Demand Letter
DISCONTINUED OPERATIONS
Loss Contingency, Damages Sought, Value	$ 44,700								$ 40,200
Settlement value of indemnification claim and other miscellaneous items					$ 500