Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for product returns
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ 7,362	$ 11,283	$ 5,804
Additions charged to Expense or Revenue	1,148	0	5,479
Deductions and write-offs	0	(3,921)	0
Balance at End of Year	8,510	7,362	11,283
Allowance for obsolescence
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	768	829	397
Additions charged to Expense or Revenue	511	1,192	2,281
Deductions and write-offs	(690)	(1,253)	(1,849)
Balance at End of Year	$ 589	$ 768	$ 829