Commitments - Off Take Sales Agreements (Details)	12 Months Ended
	Dec. 31, 2015 item lb
Commitments [Abstract]
Number of off-take sales agreements | item	10
2016 Commitment (in pounds)	662,000
2017 Commitment (in pounds)	600,000
2018 Commitment (in pounds)	500,000
2019 Commitment (in pounds)	600,000
2020 Commitment (in pounds)	450,000
2021 Commitment (in pounds)	250,000