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Intangible Assets - Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Finite-lived intangible assets
Intangible assets, gross	$ 6,051		$ 6,051		$ 6,071
Less accumulated amortization	(5,081)		(5,081)		(5,020)
Intangible assets, net	970		970		1,051
Amortization of intangible assets	100	$ 100	100	$ 200
Trade name
Finite-lived intangible assets
Intangible assets, gross	1,208		1,208		1,208
Patents and know-how
Finite-lived intangible assets
Intangible assets, gross	4,113		4,113		4,113
Customer relationships
Finite-lived intangible assets
Intangible assets, gross	$ 730		$ 730		$ 750
Minimum \| Trade name
Finite-lived intangible assets
Useful life			15 years
Minimum \| Patents and know-how
Finite-lived intangible assets
Useful life			5 years
Minimum \| Customer relationships
Finite-lived intangible assets
Useful life			4 years
Maximum \| Trade name
Finite-lived intangible assets
Useful life			20 years
Maximum \| Patents and know-how
Finite-lived intangible assets
Useful life			12 years
Maximum \| Customer relationships
Finite-lived intangible assets
Useful life			8 years