Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Doubtful Accounts [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of year		$ 489	$ 235	$ 288
Additions charged (credited) to costs and expenses		126	417	(1)
Deductions	[1]	(184)	(163)	(52)
Balance at end of year		431	489	235
Inventory Reserve [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of year		2,546	1,823	1,682
Additions charged (credited) to costs and expenses		538	905	369
Deductions	[1]	(769)	(182)	(228)
Balance at end of year		$ 2,315	$ 2,546	$ 1,823

[1] represents write-offs.