Segments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information
Revenue	$ 547,237	$ 594,235	$ 482,224	$ 498,883	$ 457,328	$ 357,748	$ 324,244	$ 287,696	$ 2,122,579	$ 1,427,016	$ 1,237,497
Costs of products sold, exclusive of depreciation and amortization shown below									1,623,358	1,020,100	874,885
Operating									246,613	223,585	224,700
General and administrative									87,845	78,597	71,918
Depreciation and amortization									98,397	66,409	48,210
Loss (gain) on disposal or impairment of long-lived assets, net	11,959	1,376	19,315	(58)	(109)	408	(376)	(162)	32,592	(239)	(3,531)
Total expenses	542,109	577,312	491,178	478,206	448,687	345,387	311,727	282,651	2,088,805	1,388,452	1,216,182
Earnings from equity method investments	15,827	14,223	19,187	14,962	12,788	7,483	14,861	17,345	64,199	52,477	36,036
Gain on issuance of common units by equity method investee	2,121	18,772	0	8,127	26,873	0	0	0	29,020	26,873	0
Operating income (loss)	23,076	49,918	10,233	43,766	48,302	19,844	27,378	22,390	126,993	117,914	57,351
Interest expense (income)									49,044	25,142	8,902
Other expense (income), net									(20,622)	44,273	21,569
Total other expenses, net	(2,196)	(6,368)	29,489	7,497	17,646	13,294	10,613	27,862	28,422	69,415	30,471
Income (loss) from continuing operations before income taxes	25,272	56,286	(19,256)	36,269	30,656	6,550	16,765	(5,472)	98,571	48,499	26,880
Additions to long-lived assets									343,164	229,318	121,255
Total assets	2,589,802				2,470,614				2,589,802	2,470,614
Equity method investments	577,920				565,124				577,920	565,124
SemStream [Member]
Segment Reporting Information
Revenue									0	0	7
Costs of products sold, exclusive of depreciation and amortization shown below									0	0	33
Operating									0	1	(37)
General and administrative									83	600	930
Depreciation and amortization									0	0	0
Loss (gain) on disposal or impairment of long-lived assets, net									0	6	214
Total expenses									83	607	1,140
Earnings from equity method investments									2,343	7,123	(403)
Gain on issuance of common units by equity method investee									29,020	26,873
Operating income (loss)									31,280	33,389	(1,536)
Interest expense (income)									(5,140)	(4,810)	(3,449)
Other expense (income), net									(34,212)	128	(21)
Total other expenses, net									(39,352)	(4,682)	(3,470)
Income (loss) from continuing operations before income taxes									70,632	38,071	1,934
Additions to long-lived assets									0	0	0
Total assets	162,246				208,847				162,246	208,847
Equity method investments	162,246				208,848				162,246	208,848
SemCAMS [Member]
Segment Reporting Information
Revenue									176,724	198,450	223,219
Costs of products sold, exclusive of depreciation and amortization shown below									344	305	768
Operating									114,587	150,319	174,284
General and administrative									17,417	14,940	14,020
Depreciation and amortization									14,295	10,766	10,589
Loss (gain) on disposal or impairment of long-lived assets, net									(950)	0	0
Total expenses									145,693	176,330	199,661
Earnings from equity method investments									0	0	0
Gain on issuance of common units by equity method investee									0	0
Operating income (loss)									31,031	22,120	23,558
Interest expense (income)									13,558	18,928	18,727
Other expense (income), net									20	(20)	14
Total other expenses, net									13,578	18,908	18,741
Income (loss) from continuing operations before income taxes									17,453	3,212	4,817
Additions to long-lived assets									35,286	56,122	13,340
Total assets	279,191				306,001				279,191	306,001
Equity method investments	0				0				0	0
SemGas [Member]
Segment Reporting Information
Revenue									380,183	231,119	127,870
Costs of products sold, exclusive of depreciation and amortization shown below									276,852	169,800	100,677
Operating									32,296	20,200	12,712
General and administrative									9,228	7,971	6,195
Depreciation and amortization									26,353	14,517	7,043
Loss (gain) on disposal or impairment of long-lived assets, net									20,092	665	46
Total expenses									364,821	213,153	126,673
Earnings from equity method investments									0	0	0
Gain on issuance of common units by equity method investee									0	0
Operating income (loss)									15,362	17,966	1,197
Interest expense (income)									8,570	3,268	1,461
Other expense (income), net									0	(3)	0
Total other expenses, net									8,570	3,265	1,461
Income (loss) from continuing operations before income taxes									6,792	14,701	(264)
Additions to long-lived assets									166,207	97,021	47,140
Total assets	662,223				552,095				662,223	552,095
Equity method investments	0				0				0	0
SemLogistics [Member]
Segment Reporting Information
Revenue									12,650	11,671	12,341
Costs of products sold, exclusive of depreciation and amortization shown below									615	380	196
Operating									8,361	7,444	5,921
General and administrative									6,139	5,854	5,652
Depreciation and amortization									10,005	9,426	9,780
Loss (gain) on disposal or impairment of long-lived assets, net									(2,490)	0	0
Total expenses									22,630	23,104	21,549
Earnings from equity method investments									0	0	0
Gain on issuance of common units by equity method investee									0	0
Operating income (loss)									(9,980)	(11,433)	(9,208)
Interest expense (income)									1,528	1,435	2,486
Other expense (income), net									796	(400)	(420)
Total other expenses, net									2,324	1,035	2,066
Income (loss) from continuing operations before income taxes									(12,304)	(12,468)	(11,274)
Additions to long-lived assets									2,974	2,071	1,188
Total assets	150,498				168,835				150,498	168,835
Equity method investments	0				0				0	0
SemMexico [Member]
Segment Reporting Information
Revenue									290,869	242,559	263,870
Costs of products sold, exclusive of depreciation and amortization shown below									252,082	209,841	236,851
Operating									10,576	9,379	7,677
General and administrative									12,125	10,700	9,433
Depreciation and amortization									6,031	5,991	6,171
Loss (gain) on disposal or impairment of long-lived assets, net									(53)	(854)	(290)
Total expenses									280,761	235,057	259,842
Earnings from equity method investments									0	0	0
Gain on issuance of common units by equity method investee									0	0
Operating income (loss)									10,108	7,502	4,028
Interest expense (income)									166	188	314
Other expense (income), net									(11)	(652)	(38)
Total other expenses, net									155	(464)	276
Income (loss) from continuing operations before income taxes									9,953	7,966	3,752
Additions to long-lived assets									9,690	6,375	3,396
Total assets	107,225				104,154				107,225	104,154
Equity method investments	0				0				0	0
Corporate and other [Member]
Segment Reporting Information
Revenue									(37,897)	(23,985)	(10,607)
Costs of products sold, exclusive of depreciation and amortization shown below									(37,897)	(23,985)	(10,606)
Operating									0	0	0
General and administrative									22,502	21,766	22,367
Depreciation and amortization									1,678	2,001	2,496
Loss (gain) on disposal or impairment of long-lived assets, net									15,674	0	0
Total expenses									1,957	(218)	14,257
Earnings from equity method investments									0	0	0
Gain on issuance of common units by equity method investee									0	0
Operating income (loss)									(39,854)	(23,767)	(24,864)
Interest expense (income)									(710)	(8,790)	(10,228)
Other expense (income), net									12,306	45,234	22,003
Total other expenses, net									11,596	36,444	11,775
Income (loss) from continuing operations before income taxes									(51,450)	(60,211)	(36,639)
Additions to long-lived assets									1,672	734	14,827
Total assets	69,780				60,198				69,780	60,198
Equity method investments	0				0				0	0
Crude [Member]
Segment Reporting Information
Revenue									1,300,050	767,202	620,797
Costs of products sold, exclusive of depreciation and amortization shown below									1,131,362	663,759	546,966
Operating									80,793	36,242	24,143
General and administrative									20,351	16,766	13,321
Depreciation and amortization									40,035	23,708	12,131
Loss (gain) on disposal or impairment of long-lived assets, net									319	(56)	(3,501)
Total expenses									1,272,860	740,419	593,060
Earnings from equity method investments									61,856	45,354	36,439
Gain on issuance of common units by equity method investee									0	0
Operating income (loss)									89,046	72,137	64,176
Interest expense (income)									31,072	14,923	(409)
Other expense (income), net									479	(14)	31
Total other expenses, net									31,551	14,909	(378)
Income (loss) from continuing operations before income taxes									57,495	57,228	64,554
Additions to long-lived assets									127,335	66,995	41,364
Total assets	1,158,639				1,070,484				1,158,639	1,070,484
Equity method investments	415,674				356,276				415,674	356,276
Operating Segments [Member]
Segment Reporting Information
Revenue									2,122,579	1,427,016	1,237,497
Operating Segments [Member] | SemStream [Member]
Segment Reporting Information
Revenue									0	0	7
Operating Segments [Member] | SemCAMS [Member]
Segment Reporting Information
Revenue									176,724	198,450	223,219
Operating Segments [Member] | SemGas [Member]
Segment Reporting Information
Revenue									342,286	207,134	117,264
Operating Segments [Member] | SemLogistics [Member]
Segment Reporting Information
Revenue									12,650	11,671	12,341
Operating Segments [Member] | SemMexico [Member]
Segment Reporting Information
Revenue									290,869	242,559	263,870
Operating Segments [Member] | Corporate and other [Member]
Segment Reporting Information
Revenue									0	0	(1)
Operating Segments [Member] | Crude [Member]
Segment Reporting Information
Revenue									1,300,050	767,202	620,797
Intersegment Eliminations [Member]
Segment Reporting Information
Revenue									0	0	0
Intersegment Eliminations [Member] | SemStream [Member]
Segment Reporting Information
Revenue									0	0	0
Intersegment Eliminations [Member] | SemCAMS [Member]
Segment Reporting Information
Revenue									0	0	0
Intersegment Eliminations [Member] | SemGas [Member]
Segment Reporting Information
Revenue									37,897	23,985	10,606
Intersegment Eliminations [Member] | SemLogistics [Member]
Segment Reporting Information
Revenue									0	0	0
Intersegment Eliminations [Member] | SemMexico [Member]
Segment Reporting Information
Revenue									0	0	0
Intersegment Eliminations [Member] | Corporate and other [Member]
Segment Reporting Information
Revenue									(37,897)	(23,985)	(10,606)
Intersegment Eliminations [Member] | Crude [Member]
Segment Reporting Information
Revenue									$ 0	$ 0	$ 0