Segments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Segment Reporting Information
Revenues, External	$ 324,244	$ 331,777	$ 611,940	$ 643,808
Revenues, Intersegment
Total revenues	324,244	331,777	611,940	643,808
Costs of products sold, exclusive of depreciation and amortization shown below	212,709	219,936	425,078	461,457
Operating	69,682	82,389	110,453	120,380
General and administrative	16,898	16,561	33,935	36,391
Depreciation and amortization	12,814	11,882	25,450	23,607
Gain on disposal of long-lived assets, net	(376)	119	(538)	119
Total expenses	311,727	330,887	594,378	641,954
Earnings from equity method investments	14,861	12,289	32,206	19,787
Operating income	27,378	13,179	49,768	21,641
Other expenses (income), net	10,613	5,587	38,475	13,203
Income (loss) from continuing operations before income taxes	16,765	7,592	11,293	8,438
Total assets (excluding intersegment receivables)	2,096,651		2,096,651		1,748,179
Crude [Member]
Segment Reporting Information
Revenues, External	161,422	157,418	332,654	337,133
Revenues, Intersegment			0
Total revenues	161,422	157,418	332,654	337,133
Costs of products sold, exclusive of depreciation and amortization shown below	140,506	140,549	288,957	301,057
Operating	5,691	6,462	11,429	11,916
General and administrative	3,568	2,063	7,418	4,781
Depreciation and amortization	3,690	2,999	7,197	5,966
Gain on disposal of long-lived assets, net	(25)	56	(25)	56
Total expenses	153,430	152,129	314,976	323,776
Earnings from equity method investments	10,661	8,461	21,090	15,032
Operating income	18,653	13,750	38,768	28,389
Other expenses (income), net	4,120	(383)	7,291	(620)
Income (loss) from continuing operations before income taxes	14,533	14,133	31,477	29,009
Total assets (excluding intersegment receivables)	867,993		867,993
SemStream [Member]
Segment Reporting Information
Revenues, External	0		0	6
Revenues, Intersegment			0
Total revenues	0			6
Costs of products sold, exclusive of depreciation and amortization shown below		3	0	37
Operating	0	(21)	1	(27)
General and administrative	160	(1)	316	50
Depreciation and amortization	0		0
Gain on disposal of long-lived assets, net	0		6
Total expenses	160	(19)	323	60
Earnings from equity method investments	4,200	3,828	11,116	4,755
Operating income	4,040	3,847	10,793	4,701
Other expenses (income), net	(1,193)	7	(2,161)	45
Income (loss) from continuing operations before income taxes	5,233	3,840	12,954	4,656
Total assets (excluding intersegment receivables)	176,816		176,816
SemCAMS [Member]
Segment Reporting Information
Revenues, External	66,459	79,683	102,240	114,848
Revenues, Intersegment			0
Total revenues	66,459	79,683	102,240	114,848
Costs of products sold, exclusive of depreciation and amortization shown below	1	71	184	190
Operating	55,508	68,848	82,392	95,084
General and administrative	3,342	2,632	7,487	7,050
Depreciation and amortization	2,638	2,673	5,294	5,246
Gain on disposal of long-lived assets, net			0
Total expenses	61,489	74,224	95,357	107,570
Earnings from equity method investments			0
Operating income	4,970	5,459	6,883	7,278
Other expenses (income), net	4,748	5,352	9,459	10,555
Income (loss) from continuing operations before income taxes	222	107	(2,576)	(3,277)
Total assets (excluding intersegment receivables)	298,793		298,793
SemGas [Member]
Segment Reporting Information
Revenues, External	41,908	23,580	76,562	54,290
Revenues, Intersegment	5,018	2,554	9,103	5,284
Total revenues	46,926	26,134	85,665	59,574
Costs of products sold, exclusive of depreciation and amortization shown below	33,567	19,990	62,738	46,539
Operating	4,289	3,306	8,433	6,159
General and administrative	1,598	1,394	3,189	3,237
Depreciation and amortization	2,233	1,726	4,361	3,356
Gain on disposal of long-lived assets, net	(4)		(6)
Total expenses	41,683	26,416	78,715	59,291
Earnings from equity method investments			0
Operating income	5,243	(282)	6,950	283
Other expenses (income), net	676	770	1,269	1,302
Income (loss) from continuing operations before income taxes	4,567	(1,052)	5,681	(1,019)
Total assets (excluding intersegment receivables)	156,724		156,724
SemLogistics [Member]
Segment Reporting Information
Revenues, External	2,623	2,613	5,658	6,397
Revenues, Intersegment			0
Total revenues	2,623	2,613	5,658	6,397
Costs of products sold, exclusive of depreciation and amortization shown below		99	0	99
Operating	1,848	1,631	3,687	3,085
General and administrative	1,486	1,448	2,606	3,259
Depreciation and amortization	2,313	2,334	4,653	4,652
Gain on disposal of long-lived assets, net			0
Total expenses	5,647	5,512	10,946	11,095
Earnings from equity method investments			0
Operating income	(3,024)	(2,899)	(5,288)	(4,698)
Other expenses (income), net	357	189	1,113	1,468
Income (loss) from continuing operations before income taxes	(3,381)	(3,088)	(6,401)	(6,166)
Total assets (excluding intersegment receivables)	160,490		160,490
SemMexico [Member]
Segment Reporting Information
Revenues, External	51,832	68,483	94,826	131,134
Revenues, Intersegment			0
Total revenues	51,832	68,483	94,826	131,134
Costs of products sold, exclusive of depreciation and amortization shown below	43,653	61,778	82,302	118,819
Operating	2,346	2,163	4,511	4,163
General and administrative	2,443	2,541	4,665	5,229
Depreciation and amortization	1,458	1,517	2,938	3,078
Gain on disposal of long-lived assets, net	(347)	63	(513)	63
Total expenses	49,553	68,062	93,903	131,352
Earnings from equity method investments			0
Operating income	2,279	421	923	(218)
Other expenses (income), net	153	425	(318)	315
Income (loss) from continuing operations before income taxes	2,126	(4)	1,241	(533)
Total assets (excluding intersegment receivables)	100,910		100,910
Corporate and Other [Member]
Segment Reporting Information
Revenues, External	0		0
Revenues, Intersegment	(5,018)	(2,554)	(9,103)	(5,284)
Total revenues	(5,018)	(2,554)	(9,103)	(5,284)
Costs of products sold, exclusive of depreciation and amortization shown below	(5,018)	(2,554)	(9,103)	(5,284)
Operating			0
General and administrative	4,301	6,484	8,254	12,785
Depreciation and amortization	482	633	1,007	1,309
Gain on disposal of long-lived assets, net			0
Total expenses	(235)	4,563	158	8,810
Earnings from equity method investments			0
Operating income	(4,783)	(7,117)	(9,261)	(14,094)
Other expenses (income), net	1,752	(773)	21,822	138
Income (loss) from continuing operations before income taxes	(6,535)	(6,344)	(31,083)	(14,232)
Total assets (excluding intersegment receivables)	$ 334,925		$ 334,925