Income Taxes - Deferred taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred Income Tax Assets
Accounts receivable allowances	$ 751	$ 760
Environmental liability	9,414	9,943
Asset retirement obligation	2,146	2,344
Deferred financing obligation	11,394	11,405
UNICAP, Current	8	56
Lease liability	44,578
Other	1,471	1,384
Federal net operating loss carryforwards	18,505	14,811
State net operating loss carryforwards	1,134	1,087
Tax credit carryforward	691	284
Total deferred tax assets	90,092	42,074
Valuation allowance, noncurrent	(3,299)	(3,138)
Total deferred tax assets, net	86,793	38,936
Deferred Income Tax Liabilities
Property and equipment, Long-Term	(74,031)	(69,356)
Land	(12,353)	(12,189)
Other deferred tax liabilities	(748)
Right of use assets	(42,536)
Intangible assets	4	247
Total deferred tax liabilities	(129,672)	(81,792)
Net deferred tax assets (liabilities)	$ (42,879)	$ (42,856)