SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Allowance for Sales Returns and Exchanges (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Sales Returns and Exchanges	$ 9,003	$ 9,916	$ 7,861	$ 8,583
Additions to the allowance	12,121	14,494	9,325
Deductions against the allowance	$ (13,034)	$ (12,439)	$ (10,047)