Income Taxes - Deferred taxes (Details) - USD ($) $ in Thousands |
Dec. 31, 2016 |
Dec. 31, 2015 |
|---|---|---|
| Deferred Income Tax Assets | ||
| Accounts receivable allowances | $ 1,921 | $ 2,097 |
| Environmental liability | 15,478 | 17,814 |
| Asset retirement obligation | 3,313 | 3,132 |
| Deferred financing obligation | 16,912 | 3,028 |
| Deferred rent | 40 | |
| UNICAP, Current | 225 | 747 |
| Other | 2,009 | 1,449 |
| Federal net operating loss carryforwards | 5,879 | 13,930 |
| State net operating loss carryforwards | 1,160 | 2,684 |
| Federal tax credit carryforward | 761 | |
| Total deferred tax assets, Long-Term | 46,897 | 45,682 |
| Valuation allowance, noncurrent | (2,707) | (975) |
| Total deferred tax assets, net | 44,190 | 44,707 |
| Deferred Income Tax Liabilities | ||
| Property and equipment, Long-Term | (84,494) | (104,798) |
| Land | (14,119) | (11,527) |
| Intangible assets | 11,631 | 13,218 |
| Total deferred tax liabilities | (110,244) | (129,543) |
| Net deferred tax assets (liabilities) | $ (66,054) | $ (84,836) |