ACQUISITIONS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Goodwill	$ 171,745	$ 198,598	$ 239,256
OilCareers [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred, Other	300
Business Combination, Consideration Transferred	26,100
Business Acquisition, Goodwill, Expected Tax Deductible Amount	1,200
Accounts receivable	1,082
Acquired intangible assets	14,508
Goodwill	15,078
Fixed assets	98
Other assets	196
Assets acquired	30,962
Accounts payable and accrued expenses	567
Deferred revenue	1,081
Deferred income taxes	2,916
Liabilities assumed	4,564
Net assets acquired	$ 26,398
Technology-Based Intangible Assets [Member] | OilCareers [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	9 months
Trademarks and Trade Names [Member] | OilCareers [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	2 years
Customer Lists [Member] | OilCareers [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	7 years
Candidate Database [Member] | OilCareers [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	2 years