Segment Information - Segment Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Segment Information
Assets	$ 820,616	$ 775,218
Business operating segments
Segment Information
Assets	500,500	473,301
Business operating segments | Activated Carbon
Segment Information
Assets	407,890	387,117
Business operating segments | Alternative Materials
Segment Information
Assets	73,558	67,394
Business operating segments | Advanced Water Purification
Segment Information
Assets	19,052	18,790
Unallocated
Segment Information
Assets	$ 320,116	$ 301,917