Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Statement Of Cash Flows [Abstract]
Net cash flows used in operating activities	$ (11,350)	$ (10,562)
Cash flows from investing activities:
Purchases of property, plant and equipment	(5,934)	(6,229)
Proceeds from sale of investment in joint venture	0	1,000
Purchases of long-term marketable securities	(91)	(56)
Proceeds from sale of long-term marketable securities	186	87
Net cash flows used in investing activities	(5,839)	(5,198)
Cash flows from financing activities:
Dividends paid	(35)	(2,235)
Repayment of debt	(496)	(997)
Proceeds from Revolving Credit and Security Agreement	19,971	8,300
Proceeds from credit facility	0	8,795
Payments on credit facility	0	(15,941)
Net cash flows provided by (used in) financing activities	19,440	(2,078)
Effect of exchange rate changes on cash and cash equivalents	(803)	784
Net increase (decrease) in cash and cash equivalents	1,448	(17,054)
Cash and cash equivalents at beginning of period	20,700	38,579
Cash and cash equivalents at end of period	22,148	21,525
Supplemental information:
Income tax payments	918	769
Interest payments	830	796
Non-cash investing activities:
Purchases of property, plant and equipment included in accounts payable	$ 1,200	$ 1,223