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 and returns
Changes in Valuation and Qualifying Accounts
Balance at Beginning of Period	$ 77		$ 390
Charged to Costs and Expenses		$ 106
Deductions	(77)	(29)	(390)
Balance at End of Period		77
Inventory reserves
Changes in Valuation and Qualifying Accounts
Balance at Beginning of Period	8,897	10,465	23,642
Charged to Costs and Expenses	8,135	1,051	1,721
Deductions	(2,820)	(2,619)	(14,898)
Balance at End of Period	$ 14,212	$ 8,897	$ 10,465