Revenue Recognition - Cumulative Effect from Adoption of New Accounting Standard (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets:
Trade and other accounts receivable, net of allowance	$ 30,022	$ 31,870	$ 31,643
Inventories	39,621	31,798	32,228
Liabilities and Stockholders’ Equity:
Accounts payable and accrued liabilities	18,870	32,795	32,758
Deferred revenue and customer deposits	4,101	6,151	6,669
Accumulated deficit	$ (277,185)	(246,955)	$ (247,233)
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Assets:
Trade and other accounts receivable, net of allowance		227
Inventories		(430)
Liabilities and Stockholders’ Equity:
Accounts payable and accrued liabilities		37
Deferred revenue and customer deposits		(518)
Accumulated deficit		$ 278