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Derivative Instruments	3 Months Ended
Derivative Instruments	Mar. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments	Derivative Instruments The Company enters into natural gas swap contracts to hedge the exposure to variability in expected future cash flows associated with the fluctuations in the price of natural gas related to the Company’s forecasted sales. As of March 31, 2018 and December 31, 2017, the Company had natural gas swap contracts outstanding with notional amounts totaling 6,300 million and 8,400 million British thermal units maturing in the fourth quarter of 2018, respectively. The Company’s natural gas swap contracts economically hedge certain risk but are not designated as hedges for financial reporting purposes. All changes in the fair value of these derivative instruments are recorded as other revenues in the Condensed Statements of Operations. The Company records all derivative instruments at fair value and had an asset of $1.3 million and $1.7 million related to natural gas swap contracts outstanding as of March 31, 2018 and December 31, 2017, respectively, included in prepaid expenses in the accompanying Condensed Balance Sheets.