Segments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Revenue	$ 377,226	$ 482,224	$ 675,536	$ 981,107
Costs of products sold, exclusive of depreciation and amortization shown below	244,158	368,527	436,230	753,640
Operating	60,800	59,424	113,890	110,202
General and administrative	22,917	21,850	55,227	40,586
Depreciation and amortization	24,674	22,062	48,408	45,699
Loss (gain) on disposal of long-lived assets, net	1,372	19,315	2,430	19,257
Total expenses	353,921	491,178	656,185	969,384
Earnings from equity method investments	23,903	19,187	44,462	34,149
Gain on issuance of common units by equity method investee	5,897	0	5,897	8,127
Operating income	53,105	10,233	69,710	53,999
Other expenses (income), net	9,809	29,489	15,896	36,986
Income (loss) from continuing operations before income taxes	43,296	(19,256)	53,814	17,013
Total assets at June 30, 2015 (excluding intersegment receivables)	2,949,389		2,949,389		$ 2,589,802
Crude [Member]
Segment Reporting Information [Line Items]
Revenue	223,303	292,156	364,971	584,670
Costs of products sold, exclusive of depreciation and amortization shown below	173,133	255,745	278,278	510,282
Operating	23,955	17,689	45,117	32,828
General and administrative	6,332	6,438	11,954	10,380
Depreciation and amortization	10,608	7,276	20,751	18,758
Loss (gain) on disposal of long-lived assets, net	(79)	(27)	73	(61)
Total expenses	213,949	287,121	356,173	572,187
Earnings from equity method investments	17,683	14,219	38,547	25,590
Gain on issuance of common units by equity method investee	0		0
Operating income	27,037	19,254	47,345	38,073
Other expenses (income), net	13,083	5,178	23,729	9,841
Income (loss) from continuing operations before income taxes	13,954	14,076	23,616	28,232
Total assets at June 30, 2015 (excluding intersegment receivables)	1,407,189		1,407,189
SemStream [Member]
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Costs of products sold, exclusive of depreciation and amortization shown below	0	0	0	0
Operating	0	0	0	0
General and administrative	12	(52)	15	61
Depreciation and amortization	0	0	0	0
Loss (gain) on disposal of long-lived assets, net	0	0	0	0
Total expenses	12	(52)	15	61
Earnings from equity method investments	6,220	4,968	5,915	8,559
Gain on issuance of common units by equity method investee	5,897		5,897	8,127
Operating income	12,105	5,020	11,797	16,625
Other expenses (income), net	(7,959)	(1,277)	(17,175)	(2,541)
Income (loss) from continuing operations before income taxes	20,064	6,297	28,972	19,166
Total assets at June 30, 2015 (excluding intersegment receivables)	122,773		122,773
SemCAMS [Member]
Segment Reporting Information [Line Items]
Revenue	35,915	39,954	65,639	79,237
Costs of products sold, exclusive of depreciation and amortization shown below	76	71	208	138
Operating	23,665	28,836	41,996	52,502
General and administrative	4,193	3,574	7,569	7,554
Depreciation and amortization	3,187	3,079	6,253	5,908
Loss (gain) on disposal of long-lived assets, net	0	(915)	0	(915)
Total expenses	31,121	34,645	56,026	65,187
Earnings from equity method investments	0	0	0	0
Gain on issuance of common units by equity method investee	0		0	0
Operating income	4,794	5,309	9,613	14,050
Other expenses (income), net	3,263	3,750	6,332	7,905
Income (loss) from continuing operations before income taxes	1,531	1,559	3,281	6,145
Total assets at June 30, 2015 (excluding intersegment receivables)	282,551		282,551
SemGas [Member]
Segment Reporting Information [Line Items]
Revenue	66,721	92,954	132,978	193,532
Costs of products sold, exclusive of depreciation and amortization shown below	36,160	68,231	77,429	146,813
Operating	8,799	8,012	16,845	15,456
General and administrative	2,641	2,240	4,704	4,212
Depreciation and amortization	7,359	7,279	14,497	12,248
Loss (gain) on disposal of long-lived assets, net	1,450	20,100	1,449	20,104
Total expenses	56,409	105,862	114,924	198,833
Earnings from equity method investments	0	0	0	0
Gain on issuance of common units by equity method investee	0		0	0
Operating income	10,312	(12,908)	18,054	(5,301)
Other expenses (income), net	3,269	2,013	6,120	3,702
Income (loss) from continuing operations before income taxes	7,043	(14,921)	11,934	(9,003)
Total assets at June 30, 2015 (excluding intersegment receivables)	709,818		709,818
SemLogistics [Member]
Segment Reporting Information [Line Items]
Revenue	6,279	3,981	11,431	8,771
Costs of products sold, exclusive of depreciation and amortization shown below	0	265	0	615
Operating	2,041	1,940	4,655	4,020
General and administrative	2,246	1,529	3,923	2,951
Depreciation and amortization	2,154	2,555	4,194	5,050
Loss (gain) on disposal of long-lived assets, net	0	(3,634)	0	(3,634)
Total expenses	6,441	2,655	12,772	9,002
Earnings from equity method investments	0	0	0	0
Gain on issuance of common units by equity method investee	0		0	0
Operating income	(162)	1,326	(1,341)	(231)
Other expenses (income), net	(432)	83	684	334
Income (loss) from continuing operations before income taxes	270	1,243	(2,025)	(565)
Total assets at June 30, 2015 (excluding intersegment receivables)	154,432		154,432
SemMexico [Member]
Segment Reporting Information [Line Items]
Revenue	51,459	62,971	112,949	134,581
Costs of products sold, exclusive of depreciation and amortization shown below	41,240	54,007	92,747	115,476
Operating	2,340	2,947	5,277	5,396
General and administrative	2,823	3,112	4,765	5,863
Depreciation and amortization	1,037	1,456	2,090	2,883
Loss (gain) on disposal of long-lived assets, net	0		(19)	(28)
Total expenses	47,440	61,522	104,860	129,590
Earnings from equity method investments	0	0	0	0
Gain on issuance of common units by equity method investee	0		0	0
Operating income	4,019	1,449	8,089	4,991
Other expenses (income), net	56	(56)	125	(101)
Income (loss) from continuing operations before income taxes	3,963	1,505	7,964	5,092
Total assets at June 30, 2015 (excluding intersegment receivables)	97,011		97,011
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenue	(6,451)	(9,792)	(12,432)	(19,684)
Costs of products sold, exclusive of depreciation and amortization shown below	(6,451)	(9,792)	(12,432)	(19,684)
Operating		0	0	0
General and administrative	4,670	5,009	22,297	9,565
Depreciation and amortization	329	417	623	852
Loss (gain) on disposal of long-lived assets, net	1	3,791	927	3,791
Total expenses	(1,451)	(575)	11,415	(5,476)
Earnings from equity method investments	0	0	0	0
Gain on issuance of common units by equity method investee	0		0	0
Operating income	(5,000)	(9,217)	(23,847)	(14,208)
Other expenses (income), net	(1,471)	19,798	(3,919)	17,846
Income (loss) from continuing operations before income taxes	(3,529)	(29,015)	(19,928)	(32,054)
Total assets at June 30, 2015 (excluding intersegment receivables)	175,615		175,615
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue	377,226	482,224	675,536	981,107
Operating Segments [Member] | Crude [Member]
Segment Reporting Information [Line Items]
Revenue	223,303	292,156	364,971	584,670
Operating Segments [Member] | SemStream [Member]
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Operating Segments [Member] | SemCAMS [Member]
Segment Reporting Information [Line Items]
Revenue	35,915	39,954	65,639	79,237
Operating Segments [Member] | SemGas [Member]
Segment Reporting Information [Line Items]
Revenue	60,270	83,162	120,546	173,848
Operating Segments [Member] | SemLogistics [Member]
Segment Reporting Information [Line Items]
Revenue	6,279	3,981	11,431	8,771
Operating Segments [Member] | SemMexico [Member]
Segment Reporting Information [Line Items]
Revenue	51,459	62,971	112,949	134,581
Operating Segments [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenue	0	0	0
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Intersegment Eliminations [Member] | Crude [Member]
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Intersegment Eliminations [Member] | SemStream [Member]
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Intersegment Eliminations [Member] | SemCAMS [Member]
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Intersegment Eliminations [Member] | SemGas [Member]
Segment Reporting Information [Line Items]
Revenue	6,451	9,792	12,432	19,684
Intersegment Eliminations [Member] | SemLogistics [Member]
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Intersegment Eliminations [Member] | SemMexico [Member]
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Intersegment Eliminations [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenue	$ (6,451)	$ (9,792)	$ (12,432)	$ (19,684)