GOODWILL AND INTANGIBLE ASSETS - Intangible Assets with Definite Lives (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Intangible assets with definite lives
Gross Carrying Amount	$ 181,755	$ 200,456
Accumulated Amortization	(159,356)	(162,627)
Total	$ 22,399	$ 37,829
Weighted-Average Useful Life (Years)	4 years 1 month 6 days	4 years 1 month 6 days
Service professional relationships
Intangible assets with definite lives
Gross Carrying Amount	$ 97,989	$ 97,160
Accumulated Amortization	(97,322)	(97,000)
Total	$ 667	$ 160
Weighted-Average Useful Life (Years)	3 years	3 years
Technology
Intangible assets with definite lives
Gross Carrying Amount	$ 82,351	$ 83,468
Accumulated Amortization	(60,619)	(47,144)
Total	$ 21,732	$ 36,324
Weighted-Average Useful Life (Years)	5 years 6 months	5 years 6 months
Memberships
Intangible assets with definite lives
Gross Carrying Amount		$ 15,900
Accumulated Amortization		(15,900)
Total		$ 0
Weighted-Average Useful Life (Years)		3 years
Customer lists and user base
Intangible assets with definite lives
Gross Carrying Amount		$ 800
Accumulated Amortization		(192)
Total		$ 608
Weighted-Average Useful Life (Years)		8 years
Trade names
Intangible assets with definite lives
Gross Carrying Amount	$ 1,415	$ 3,128
Accumulated Amortization	(1,415)	(2,391)
Total	$ 0	$ 737
Weighted-Average Useful Life (Years)	5 years	5 years 7 months 6 days