Derivative Instruments - (Details) - USD ($) $ in Thousands |
Dec. 31, 2016 |
Dec. 31, 2015 |
|---|---|---|
| Assets | ||
| Gross amounts of commodity derivative contracts recognized at fair value | $ 1,272 | $ 4,644 |
| Cash collateral | 9,366 | 5,638 |
| Total gross amount recognized | 10,638 | 10,282 |
| Gross amounts offset | (3,511) | (185) |
| Net amount reported in the Consolidated Balance Sheets | 7,127 | 10,097 |
| Liabilities | ||
| Gross amounts of commodity derivative contracts recognized at fair value | 3,511 | 185 |
| Cash collateral | 0 | 0 |
| Total gross amount recognized | 3,511 | 185 |
| Gross amounts offset | (3,511) | (185) |
| Net amount reported in the Consolidated Balance Sheets | $ 0 | $ 0 |