v3.5.0.2
Commitments and Contingencies - Natural Gas Purchases (Details)
MMBTU in Thousands
6 Months Ended
Jun. 30, 2016
USD ($)
MMBTU
Long-term Purchase Commitment [Line Items]  
Commitments to purchase natural gas $ 1,820,000
Weighted average rate per MMBtu $ 2.35
MMBtus under fixed-price contracts  
Long-term Purchase Commitment [Line Items]  
Total MMBtus under contract | MMBTU 775