Segment Reporting - Information Concerning Business Activities (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) segment	Jun. 30, 2017 USD ($)
Segment Reporting [Abstract]
Number of reportable segments | segment			3
Segment Reporting Information [Line Items]
Revenues	$ 452,417	$ 315,202	$ 839,673	$ 618,289
Segment operating (losses) earnings	4,298	619	5,375	(965)
Depreciation, depletion and amortization	2,262	3,563	4,674	7,532
Leasehold Improvements
Segment Reporting Information [Line Items]
Property and equipment additions			13
Marketing
Segment Reporting Information [Line Items]
Revenues	438,791		812,429
Inventory liquidation gains and valuation (losses)	1,900	(1,400)	2,500	(2,100)
Transportation
Segment Reporting Information [Line Items]
Revenues	13,626		27,244
Reporting Segments
Segment Reporting Information [Line Items]
Revenues	452,417	315,202	839,673	618,289
Segment operating (losses) earnings	6,582	2,079	9,942	3,132
Depreciation, depletion and amortization	2,262	3,563	4,674	7,532
Property and equipment additions	1,849	1,102	2,715	2,108
Reporting Segments | Marketing
Segment Reporting Information [Line Items]
Revenues	438,791	301,176	812,429	589,791
Segment operating (losses) earnings	5,772	1,691	8,730	3,084
Depreciation, depletion and amortization	1,336	1,977	2,833	4,046
Property and equipment additions	277	191	1,070	273
Reporting Segments | Transportation
Segment Reporting Information [Line Items]
Revenues	13,626	13,616	27,244	27,071
Segment operating (losses) earnings	810	293	1,212	(5)
Depreciation, depletion and amortization	926	1,472	1,841	3,063
Property and equipment additions	1,572	(92)	1,645	10
Reporting Segments | Oil and Gas
Segment Reporting Information [Line Items]
Revenues	0	410	0	1,427
Segment operating (losses) earnings	0	95	0	53
Depreciation, depletion and amortization	0	114	0	423
Property and equipment additions	$ 0	$ 1,003	$ 0	$ 1,825