SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for doubtful accounts, sales returns and cash discounts
Changes to valuation allowance
Balance at beginning of period	$ 1,121	$ 1,248	$ 1,704
Charged to cost and expenses	8,364	7,389	8,407
Deductions	(8,380)	(7,516)	(8,863)
Balance at end of period	1,105	1,121	1,248
Allowance on Deferred Tax Assets and Unrecognized Tax Benefits
Changes to valuation allowance
Balance at beginning of period	26,086	17,846	19,786
Charged to cost and expenses	14,594	8,240	(1,940)
Balance at end of period	$ 40,680	$ 26,086	$ 17,846