SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES , IMPACT OF ADOPTION (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Selling and marketing expense	$ 112,965	$ 91,726	$ 201,455	$ 168,128
Net income	43,835	$ 22,184	96,066	$ 44,314
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	181		138
Accounting Standards Update 2016-09 [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Selling and marketing expense	1,000		5,000
Accounting Standards Update 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net income	$ 1,000		$ 4,000
Earnings per share, basic and diluted (usd per share)	$ 0.02		$ 0.11