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Discontinued Operations (Details) - USD ($) $ in Thousands	3 Months Ended
Discontinued Operations (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale	$ 485		$ 485
Accrued severance charges			$ 376
Loss from discontinued operations	(25)	$ (730)
Fuel Conversion Segment
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Expected severance costs	581
Fuel Conversion Segment \| Period One
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Severance costs	0
Fuel Conversion Segment \| Period Two
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cost remaining	311
Fuel Conversion Segment \| Period Three
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cost remaining	65
Fuel Conversion Segment \| Accrued Liabilities
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Accrued severance charges	$ 281