Commitments and Contingencies - Natural Gas Purchases (Details) MMBTU in Thousands |
9 Months Ended |
|---|---|
|
Sep. 30, 2016
USD ($)
MMBTU
| |
| Long-term Purchase Commitment [Line Items] | |
| Commitments to purchase natural gas | $ 1,768,000 |
| Weighted average rate per MMBtu | $ 2.85 |
| MMBtus under fixed-price contracts | |
| Long-term Purchase Commitment [Line Items] | |
| MMBtus under fixed-price contracts | MMBTU | 620 |