Other Assets - Other Noncurrent Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Summary of other noncurrent assets
Spare parts inventory	$ 3,532	$ 2,922
Catalysts	4,479	5,742
Deposits	2,392	2,370
Other	2,227	785
Total	$ 12,630	$ 11,819