Segment Reporting - Depreciation and Amortization (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014
Depreciation and amortization
Depreciation and amortization	$ 924	$ 1,007
Catalyst
Depreciation and amortization
Depreciation and amortization	170	135
Heavy Duty Diesel Systems
Depreciation and amortization
Depreciation and amortization	$ 754	$ 872

The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3602-108585

Name:	us-gaap_DepreciationDepletionAndAmortization
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration