Segments (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenue		$ 314,851	$ 298,310
Depreciation and amortization		24,047	23,734
Earnings from equity method investments		23,071	20,559
Total assets		2,801,832		$ 2,853,909
Income tax expense (benefit)		(21,407)	4,742
Net unrealized loss (gain) related to derivative instruments		(4,548)	2,645
Interest expense		18,935	14,591
Foreign currency transaction loss (gain)		1,469	(519)
Loss (gain) on sale or impairment of equity method investment		39,764	(7,894)
Other income, net		(187)	(91)
Loss from discontinued operations, net of taxes		2	0
Net income (loss)		(6,248)	5,776
Equity method investments		503,914		551,078
Crude Transportation [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization		5,859	8,618
Earnings from equity method investments		20,839	20,864
Total assets		900,365		877,017
Segment profit	[1]	25,418	24,524
Equity method investments		433,572		438,291
SemStream [Member]
Segment Reporting Information [Line Items]
Earnings from equity method investments	[2]	2,191	(305)
Total assets		70,342		112,787
Segment profit	[1]	2,181	(308)
Equity method investments		70,342		112,787
SemCAMS [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization		3,951	3,066
Total assets		372,467		331,749
Income tax expense (benefit)		965	551
Segment profit	[1]	9,904	7,885
SemGas [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization		8,922	7,138
Total assets		700,881		719,789
Segment profit	[1]	(992)	14,880
SemLogistics [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization		1,960	2,040
Total assets		153,939		155,794
Income tax expense (benefit)		59	(369)
Segment profit	[1]	2,659	861
SemMexico [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization		941	1,053
Total assets		86,453		89,608
Income tax expense (benefit)		607	990
Segment profit	[1]	2,318	5,123
Crude Facilities [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization		1,884	1,369
Total assets		152,361		155,186
Segment profit	[1]	9,587	8,402
Crude Supply and Logistics [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization		40	39
Total assets		297,163		328,419
Segment profit	[1]	9,093	5,181
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization		490	411
Total assets		67,861		83,560
Income tax expense (benefit)		(23,038)	3,570
Segment profit	[1]	(8,341)	(23,564)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization		24,047	23,734
Earnings from equity method investments		23,030	20,559
Total assets		2,801,832		$ 2,853,909
Income tax expense (benefit)		(21,407)	4,742
Segment profit	[1]	51,827	42,984
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue		314,851	298,310
Operating Segments [Member] | Crude Transportation [Member]
Segment Reporting Information [Line Items]
Revenue		17,196	20,327
Operating Segments [Member] | SemCAMS [Member]
Segment Reporting Information [Line Items]
Revenue		30,866	29,724
Operating Segments [Member] | SemGas [Member]
Segment Reporting Information [Line Items]
Revenue		43,520	60,276
Operating Segments [Member] | SemLogistics [Member]
Segment Reporting Information [Line Items]
Revenue		6,380	5,152
Operating Segments [Member] | SemMexico [Member]
Segment Reporting Information [Line Items]
Revenue		30,134	61,490
Operating Segments [Member] | Crude Facilities [Member]
Segment Reporting Information [Line Items]
Revenue		10,133	11,405
Operating Segments [Member] | Crude Supply and Logistics [Member]
Segment Reporting Information [Line Items]
Revenue		176,622	102,961
Operating Segments [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Revenue		0	6,975
Intersegment Eliminations [Member] | Crude Transportation [Member]
Segment Reporting Information [Line Items]
Revenue		7,213	3,721
Intersegment Eliminations [Member] | SemGas [Member]
Segment Reporting Information [Line Items]
Revenue		2,746	5,981
Intersegment Eliminations [Member] | Crude Facilities [Member]
Segment Reporting Information [Line Items]
Revenue		2,746	0
Intersegment Eliminations [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Revenue		$ (12,705)	$ (9,702)

[1] (1) SemStream earnings from equity method investments includes gain (loss) on issuance of common units by equity method investee. Gains and losses on the disposal or impairment of equity investments are not reported within "earnings from equity method investments" in the condensed consolidated statements of operations and comprehensive income (loss).

[2] (1) Segment profit represents revenues excluding unrealized gains (losses) related to derivative instruments plus earnings from equity method investments less cost of sales excluding depreciation and amortization and less operating and general and administrative expenses.