SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Allowance for Sales Returns and Exchanges (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Allowance for Sales Returns and Exchanges	$ 9,916	$ 7,861	$ 8,583	$ 9,510
Additions to the allowance	14,494	9,325	8,468
Deductions against the allowance	(12,439)	(10,047)	(9,395)
Sales Returns and Allowances [Member]
Reduction for deferred revenue amounts	$ 2,400	$ 1,500	$ 3,200