Segment Reporting (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Activities by Segment [Abstract]
Revenues	$ 1,173,970	$ 1,060,340	$ 3,283,090	$ 2,977,873
Depreciation Depletion and Amortization	6,228	5,373	18,443	16,147
Segment Operating Earnings [Abstract]
General and administrative	(2,300)	(2,248)	(6,701)	(6,711)
Operating earnings	5,732	11,146	20,220	34,273
Interest income	118	33	205	103
Interest expense	(2)	(1)	(2)	(24)
Earnings from continuing operations before income taxes	5,848	11,178	20,423	34,352
Identifiable Assets By Segment [Abstract]
Assets	455,900		455,900		448,082
Operating Segments [Member]
Activities by Segment [Abstract]
Revenues	1,173,970	1,060,340	3,283,090	2,977,873
Segment operating earnings (loss)	8,032	13,394	26,921	40,984
Depreciation Depletion and Amortization	6,228	5,373	18,443	16,147
Property and Equipment Additions	10,566	6,835	22,655	23,133
Segment Operating Earnings [Abstract]
Segment operating earnings	8,032	13,394	26,921	40,984
General and administrative	(2,300)	(2,248)	(6,701)	(6,711)
Operating earnings	5,732	11,146	20,220	34,273
Interest income	118	33	205	103
Interest expense	(2)	(1)	(2)	(24)
Earnings from continuing operations before income taxes	5,848	11,178	20,423	34,352
Identifiable Assets By Segment [Abstract]
Assets	455,900		455,900		448,082
Marketing [Member] | Operating Segments [Member]
Activities by Segment [Abstract]
Revenues	1,153,249	1,039,337	3,219,457	2,915,056
Segment operating earnings (loss)	5,041	11,394	22,187	35,509
Depreciation Depletion and Amortization	2,450	1,939	7,006	5,517
Property and Equipment Additions	3,377	932	9,308	9,512
Segment Operating Earnings [Abstract]
Segment operating earnings	5,041	11,394	22,187	35,509
Identifiable Assets By Segment [Abstract]
Assets	275,239		275,239		306,693
Transportation [Member] | Operating Segments [Member]
Activities by Segment [Abstract]
Revenues	17,538	16,906	52,490	51,795
Segment operating earnings (loss)	1,464	1,248	3,594	4,479
Depreciation Depletion and Amortization	1,882	1,787	5,513	5,263
Property and Equipment Additions	5,851	1,589	6,280	3,162
Segment Operating Earnings [Abstract]
Segment operating earnings	1,464	1,248	3,594	4,479
Identifiable Assets By Segment [Abstract]
Assets	40,492		40,492		34,406
Oil and Gas [Member] | Operating Segments [Member]
Activities by Segment [Abstract]
Revenues	3,183	4,097	11,143	11,022
Segment operating earnings (loss)	1,527	752	1,140	996
Depreciation Depletion and Amortization	1,896	1,647	5,924	5,367
Property and Equipment Additions	1,338	4,314	7,067	10,459
Segment Operating Earnings [Abstract]
Segment operating earnings	1,527	752	1,140	996
Identifiable Assets By Segment [Abstract]
Assets	33,875		33,875		37,093
Other [Member] | Operating Segments [Member]
Identifiable Assets By Segment [Abstract]
Assets	$ 106,294		$ 106,294		$ 69,890