Condensed Consolidated Statements of Cash Flows (Unaudited) $ in Thousands	9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)
Statement of Cash Flows [Abstract]
Net cash flows used in operating activities	$ (15,946)	$ (13,165)
Cash flows from investing activities:
Purchases of property, plant and equipment	(9,744)	(5,519)
Proceeds from sale of property, plant and equipment	0	11
Purchase of Åkers, net of cash acquired (Note 2)	0	(27,031)
Proceeds from sale of investment in joint venture (Note 2)	1,000	0
Purchases of long-term marketable securities	(83)	(619)
Proceeds from sale of long-term marketable securities	245	619
Net cash flows used in investing activities	(8,582)	(32,539)
Cash flows from financing activities:
Dividends paid	(2,236)	(4,102)
Repayment of debt	(730)	(508)
Debt issuance costs	0	(1,091)
Proceeds from Revolving Credit and Security Agreement (Note 8)	23,339	0
Payments on Revolving Credit and Security Agreement (Note 8)	(3,000)	0
Proceeds from ASW credit facility (Note 8)	8,795	0
Payments on ASW credit facility (Note 8)	(15,941)	0
Net cash flows provided by (used in) financing activities	10,227	(5,701)
Effect of exchange rate changes on cash and cash equivalents	1,089	(192)
Net decrease in cash and cash equivalents	(13,212)	(51,597)
Cash and cash equivalents at beginning of period	38,579	95,122
Cash and cash equivalents at end of period	25,367	43,525
Supplemental information:
Income tax payments	988	3,706
Interest payments	956	1,496
Non-cash investing activities:
Purchases of property, plant and equipment included in accounts payable	1,947	2,818
Non-cash financing activities:
Issuance of common stock to acquire net assets of Åkers (Note 2)	0	22,137
Issuance of debt to acquire net assets of Åkers (Note 2)	$ 0	$ 22,619