SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES , RECENT ACCOUNTING PRONOUCEMENTS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Jan. 01, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of adoption of new accounting standard, net of tax					$ 54,464
Selling and marketing (excluding customer base amortization)	$ 89,251	$ 72,705	$ 290,706	$ 240,833
Net income	58,759	$ 34,177	154,825	$ 78,491
Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of adoption of new accounting standard, net of tax					$ 54,464
Net income			154,825
Retained Earnings [Member] | Accounting Standards Update 2016-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of adoption of new accounting standard, net of tax						$ 54,000
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues	1,000		3,000
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Accounting Standards Update 2016-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Selling and marketing (excluding customer base amortization)	100		5,000
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net income	$ (1,000)		$ (6,000)
Earnings per share, basic and diluted (usd per share)	$ (0.03)		$ (0.17)