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 |