Commitments and Contingencies - Rail Service Agreements (Details) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2015 |
Dec. 31, 2014 |
Dec. 31, 2013 |
|
| Other Commitments [Line Items] | |||
| Subcontracted rail services | $ 7,710 | $ 6,994 | $ 1,898 |
| Service Agreements, Labor Service Providers | |||
| Other Commitments [Line Items] | |||
| 2016 | 6,974 | ||
| 2017 | 5,971 | ||
| 2018 | 6,096 | ||
| 2019 | 3,719 | ||
| Total | $ 22,760 | ||