Discontinued Operations and Divestitures (Narrative) (Details) $ in Thousands				8 Months Ended	12 Months Ended
	Dec. 13, 2019 USD ($) subsidiary	Aug. 30, 2019 USD ($) subsidiary	Aug. 30, 2017 USD ($)	Aug. 30, 2017 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Oct. 31, 2019 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Non-cash share-based compensation expense					$ 986	$ 414	$ 140
Debt and pension liability assumed by buyer with divestitures					2,206	0	2,950
Loss on divestiture					0	0	(8,730)
Discontinued Operations, Disposed of by Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and cash equivalents						11,471
Discontinued Operations, Disposed of by Sale | North American Fiber Solutions
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of subsidiaries | subsidiary		2
Purchase price		$ 85,000
Maximum adjustment to purchase price								$ 5,000
Proposed purchase price reduction, that was deemed not probable					5,200
Transaction costs					5,300
Transaction costs paid					3,900
Transaction costs included in loss on disposal					3,000
Cash and cash equivalents						11,712
Net sales					90,516	161,961	183,900
Discontinued Operations, Disposed of by Sale | Metalex
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of subsidiaries | subsidiary	2
Purchase price	$ 5,000
Transaction costs					800
Transaction costs paid					200
Transaction costs included in loss on disposal					500
Net working capital adjustment period	90 days
Cash and cash equivalents						(241)
Net sales					42,801	$ 83,028	$ 82,621
Disposal Group, Held-for-sale, Not Discontinued Operations | Acoustics Europe
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net proceeds from the divestiture			$ 8,100	$ 8,100
Cash and cash equivalents			200	200
Debt and pension liability assumed by buyer with divestitures			3,000
Loss on divestiture			$ (8,700)
Net sales				$ 22,900
Adjusted EBITDA Based Performance | Discontinued Operations, Disposed of by Sale | North American Fiber Solutions
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Non-cash share-based compensation expense					500
Adjusted EBITDA Based Performance | Discontinued Operations, Disposed of by Sale | Metalex
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Non-cash share-based compensation expense					$ 100