TRANSACTION AND INTEGRATION RELATED COSTS IN CONNECTION WITH THE COMBINATION - Summary (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Stock-based compensation expense	$ 238,420	$ 264,618	$ 104,820
Cost of revenue
Business Acquisition [Line Items]
Stock-based compensation expense	2,482	1,881	2,305
Selling and marketing expense
Business Acquisition [Line Items]
Stock-based compensation expense	7,943	31,318	6,000
General and administrative expense
Business Acquisition [Line Items]
Stock-based compensation expense	188,510	192,957	77,151
Product development expense
Business Acquisition [Line Items]
Stock-based compensation expense	39,485	38,462	19,364
ANGI Homeservices
Business Acquisition [Line Items]
Transaction and integration related costs	3,584	44,101
Stock-based compensation expense	70,645	122,066
Total	74,229	166,167
Accrual for Business Combination [Roll Forward]
Accrual as of January 1	8,480	0
Costs incurred	3,584	44,101
Payments made	(12,064)	(35,621)
Accrual as of December 31	0	8,480	$ 0
ANGI Homeservices | Cost of revenue
Business Acquisition [Line Items]
Transaction and integration related costs	0	0
Stock-based compensation expense	0	0
Total	0	0
ANGI Homeservices | Selling and marketing expense
Business Acquisition [Line Items]
Transaction and integration related costs	0	7,430
Stock-based compensation expense	2,161	24,416
Total	2,161	31,846
ANGI Homeservices | General and administrative expense
Business Acquisition [Line Items]
Transaction and integration related costs	3,584	36,120
Stock-based compensation expense	61,010	83,420
Total	64,594	119,540
ANGI Homeservices | Product development expense
Business Acquisition [Line Items]
Transaction and integration related costs	0	551
Stock-based compensation expense	7,474	14,230
Total	$ 7,474	$ 14,781