Segments (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016		Jun. 30, 2015		Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenue		$ 287,377	$ 377,226	$ 602,228		$ 675,536
Depreciation and amortization		25,048	24,674	49,095		48,408
Earnings from equity method investments		17,078	23,903	40,149		44,462
Total assets		3,096,974		3,096,974				$ 2,853,909
Income tax expense (benefit)		4,658	14,861	(16,749)		19,603
Net unrealized loss (gain) related to derivative instruments		4,477	(1,415)	(71)		1,230
Interest expense		18,875	16,822	37,810		31,413
Foreign currency transaction loss (gain)		1,543	(295)	3,012		(814)
Loss (gain) on sale or impairment of equity method investment		(9,120)	(6,623)	30,644		(14,517)
Other expense (income), net		(491)	(95)	(678)		(186)
Loss from discontinued operations, net of taxes		2	2	4		2
Net income		9,931	28,433	3,683		34,209
Equity method investments		446,938		446,938				551,078
Crude Transportation [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization		6,171	9,038	12,030		17,656
Earnings from equity method investments		17,078	17,683	37,917		38,547
Total assets		931,362		931,362				877,017
Segment profit	[1]	18,161	19,983	43,579		44,507
Equity method investments		427,961		427,961				438,291
SemCAMS [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization		4,294	3,187	8,245		6,253
Total assets		376,586		376,586				331,749
Income tax expense (benefit)		451	616	1,416		1,167
Segment profit	[1]	9,000	7,981	18,904		15,866
SemGas [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization		9,194	7,359	18,116		14,497
Total assets		691,823		691,823				719,789
Segment profit	[1]	12,304	17,671	11,312		32,551
SemLogistics [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization		1,983	2,154	3,943		4,194
Total assets		143,648		143,648				155,794
Income tax expense (benefit)		(273)	167	(214)		(202)
Segment profit	[1]	2,002	1,992	4,661		2,853
SemMexico [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization		949	1,037	1,890		2,090
Total assets		86,073		86,073				89,608
Income tax expense (benefit)		194	764	801		1,754
Segment profit	[1]	2,024	5,056	4,342		10,179
Crude Facilities [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization		1,921	1,406	3,805		2,775
Total assets		154,359		154,359				155,186
Segment profit	[1]	9,371	7,963	18,958		16,365
Crude Supply and Logistics [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization		40	40	80		79
Total assets		430,297		430,297				328,419
Segment profit	[1]	10,069	10,978	19,162		16,159
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization		496	453	986		864
Earnings from equity method investments	[2]	0	12,117	2,191		11,812
Total assets	[3]	282,826		282,826				196,347
Income tax expense (benefit)		4,286	13,314	(18,752)		16,884
Segment profit	[3]	(8,008)	4,740	(14,168)		(19,132)
Equity method investments	[3]	18,977		18,977				112,787
Operating Segments [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization		25,048	24,674	49,095		48,408
Earnings from equity method investments		17,078	29,800	40,108		50,359
Total assets		3,096,974		3,096,974				$ 2,853,909
Income tax expense (benefit)		4,658	14,861	(16,749)		19,603
Segment profit		54,923	76,364	106,750	[2]	119,348	[2]
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue		287,377	377,226	602,228		675,536
Operating Segments [Member] | Crude Transportation [Member]
Segment Reporting Information [Line Items]
Revenue		15,643	22,425	32,839		42,752
Operating Segments [Member] | SemCAMS [Member]
Segment Reporting Information [Line Items]
Revenue		33,815	35,915	64,681		65,639
Operating Segments [Member] | SemGas [Member]
Segment Reporting Information [Line Items]
Revenue		48,200	60,270	91,720		120,546
Operating Segments [Member] | SemLogistics [Member]
Segment Reporting Information [Line Items]
Revenue		5,932	6,279	12,312		11,431
Operating Segments [Member] | SemMexico [Member]
Segment Reporting Information [Line Items]
Revenue		30,286	51,459	60,420		112,949
Operating Segments [Member] | Crude Facilities [Member]
Segment Reporting Information [Line Items]
Revenue		10,300	11,402	20,433		22,807
Operating Segments [Member] | Crude Supply and Logistics [Member]
Segment Reporting Information [Line Items]
Revenue		143,201	189,476	319,823		292,437
Operating Segments [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Revenue		0	0	0		6,975
Intersegment Eliminations [Member] | Crude Transportation [Member]
Segment Reporting Information [Line Items]
Revenue		5,128	3,562	12,341		7,283
Intersegment Eliminations [Member] | SemGas [Member]
Segment Reporting Information [Line Items]
Revenue		2,521	6,451	5,267		12,432
Intersegment Eliminations [Member] | Crude Facilities [Member]
Segment Reporting Information [Line Items]
Revenue		2,526	0	5,272		0
Intersegment Eliminations [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Revenue		$ (10,175)	$ (10,013)	$ (22,880)		$ (19,715)

[1] (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.

[2] (1) Includes historical earnings from equity method investment including gain (loss) on issuance of common units by equity method investee related to our investment in NGL Energy. 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). See Note 3 for additional information.

[3] (2) Corporate and Other includes amounts previously included in the SemStream segment which ceased to be a reportable segment in the second quarter of 2016. See Note 3 for additional information.