Revenue Recognition - (Textual 1) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Warranty period, minimum, in years	1 year
Trade and other accounts receivable, net of allowance	$ 29,723	$ 31,870	$ 31,643
Inventories	41,637	31,798	32,228
Accounts payable and accrued liabilities	27,300	32,795	32,758
Deferred revenue and customer deposits	4,342	6,151	6,669
Accumulated deficit	$ (267,462)	(246,955)	$ (247,233)
Standard Product Warranty, Term, Maximum	8 years
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Trade and other accounts receivable, net of allowance		227
Inventories		(430)
Accounts payable and accrued liabilities		37
Deferred revenue and customer deposits		(518)
Accumulated deficit		$ 278
Sales to Distributors | Revenue
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Percentage of revenue (less than five percent)	7.00%
Non-product Sale Arrangements | Maximum | Revenue
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Percentage of revenue (less than five percent)	5.00%