ACQUIRED INTANGIBLE ASSETS, NET (Summary of Acquired Intangible Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired		$ 76,408
Finite-Lived Intangible Assets, Accumulated Amortization		25,240
Finite-Lived Intangible Assets, Translation Adjustments		5,431
Impairment of fixed and intangible assets	$ 0	2,226	$ 9,252
Acquired intangible assets, net	$ 39,000	45,737
Technology Equipment [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired		4,561
Finite-Lived Intangible Assets, Accumulated Amortization		3,930
Finite-Lived Intangible Assets, Translation Adjustments		631
Acquired intangible assets, net		0
Trademarks, Other [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired		11,103
Finite-Lived Intangible Assets, Accumulated Amortization		7,260
Finite-Lived Intangible Assets, Translation Adjustments		2,185
Acquired intangible assets, net		1,658
Customer Lists [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired		12,887
Finite-Lived Intangible Assets, Accumulated Amortization		5,696
Finite-Lived Intangible Assets, Translation Adjustments		2,112
Acquired intangible assets, net		5,079
Candidate Database [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired		8,857
Finite-Lived Intangible Assets, Accumulated Amortization		8,354
Finite-Lived Intangible Assets, Translation Adjustments		503
Acquired intangible assets, net		0
Trademarks [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired		39,000
Finite-Lived Intangible Assets, Accumulated Amortization		0
Finite-Lived Intangible Assets, Translation Adjustments		0
Acquired intangible assets, net		$ 39,000