GOODWILL AND INTANGIBLE ASSETS - SCHEDULE OF INTANGIBLE ASSETS WITH DEFINITE LIVES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Intangible assets with definite lives
Gross Carrying Amount	$ 279,551	$ 136,974
Accumulated Amortization	(74,957)	(102,168)
Total	$ 204,594	$ 34,806
Weighted-average useful life (years)	3 years 8 months 12 days	2 years 9 months 18 days
Contractor and service professional relationships and other
Intangible assets with definite lives
Gross Carrying Amount	$ 102,997	$ 7,230
Accumulated Amortization	(13,252)	(2,612)
Total	$ 89,745	$ 4,618
Weighted-average useful life (years)	3 years	4 years 6 months
Technology
Intangible assets with definite lives
Gross Carrying Amount	$ 115,200	$ 38,602
Accumulated Amortization	(37,357)	(27,667)
Total	$ 77,843	$ 10,935
Weighted-average useful life (years)	4 years 9 months 18 days	3 years 4 months 24 days
Customer lists and user base
Intangible assets with definite lives
Gross Carrying Amount	$ 23,468	$ 12,485
Accumulated Amortization	(5,401)	(9,997)
Total	$ 18,067	$ 2,488
Weighted-average useful life (years)	2 years 2 months 12 days	3 years 8 months 12 days
Content
Intangible assets with definite lives
Gross Carrying Amount	$ 5,000	$ 14,802
Accumulated Amortization	(3,973)	(8,965)
Total	$ 1,027	$ 5,837
Weighted-average useful life (years)	5 years	4 years 3 months 18 days
Trade names
Intangible assets with definite lives
Gross Carrying Amount	$ 16,986	$ 63,855
Accumulated Amortization	(13,634)	(52,927)
Total	$ 3,352	$ 10,928
Weighted-average useful life (years)	2 years 7 months 6 days	1 year 9 months 18 days
Memberships
Intangible assets with definite lives
Gross Carrying Amount	$ 15,900
Accumulated Amortization	(1,340)
Total	$ 14,560
Weighted-average useful life (years)	3 years