Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Statement Of Cash Flows [Abstract]
Net cash flows used in operating activities	$ (8,194)	$ (15,946)
Cash flows from investing activities:
Purchases of property, plant and equipment	(8,803)	(9,744)
Proceeds from sale of investment in joint venture	0	1,000
Purchases of long-term marketable securities	(102)	(83)
Proceeds from sale of long-term marketable securities	247	245
Net cash flows used in investing activities	(8,658)	(8,582)
Cash flows from financing activities:
Dividends paid	(35)	(2,236)
Deferred financing costs (Note 7)	(477)	0
Repayment of debt	(132)	(730)
Proceeds from Revolving Credit and Security Agreement	23,000	23,339
Payments on Revolving Credit and Security Agreement	(29,500)	(3,000)
Proceeds from sale and leaseback financing arrangement (Note 7)	19,000	0
Repayments on sale and leaseback financing arrangement (Note 7)	(141)	0
Proceeds from credit facility	0	8,795
Payments on credit facility	0	(15,941)
Net cash flows provided by financing activities	11,715	10,227
Effect of exchange rate changes on cash and cash equivalents	(785)	1,089
Net decrease in cash and cash equivalents	(5,922)	(13,212)
Cash and cash equivalents at beginning of period	20,700	38,579
Cash and cash equivalents at end of period	14,778	25,367
Supplemental information:
Income tax payments	1,126	988
Interest payments	1,338	956
Non-cash investing activities:
Purchases of property, plant and equipment included in accounts payable	$ 1,161	$ 1,947