Segments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Revenue	$ 298,310us-gaap_Revenues	$ 498,883us-gaap_Revenues
Costs of products sold, exclusive of depreciation and amortization shown below	192,072us-gaap_CostOfGoodsSold	385,113us-gaap_CostOfGoodsSold
Operating	53,090us-gaap_OperatingCostsAndExpenses	50,778us-gaap_OperatingCostsAndExpenses
General and administrative	32,310us-gaap_GeneralAndAdministrativeExpense	18,736us-gaap_GeneralAndAdministrativeExpense
Depreciation and amortization	23,734us-gaap_DepreciationAndAmortization	23,637us-gaap_DepreciationAndAmortization
Loss (gain) on disposal of long-lived assets, net	1,058us-gaap_GainLossOnDispositionOfAssets	(58)us-gaap_GainLossOnDispositionOfAssets
Total expenses	302,264us-gaap_CostsAndExpenses	478,206us-gaap_CostsAndExpenses
Earnings from equity method investments	20,559	14,962
Gain on issuance of common units by equity method investee	0	8,127
Operating income	16,605us-gaap_OperatingIncomeLoss	43,766us-gaap_OperatingIncomeLoss
Other expenses (income), net	6,087us-gaap_NonoperatingIncomeExpense	7,497us-gaap_NonoperatingIncomeExpense
Income (loss) from continuing operations before income taxes	10,518	36,269
Total assets at March 31, 2015 (excluding intersegment receivables)	2,861,540us-gaap_Assets		2,589,802us-gaap_Assets
Crude [Member]
Segment Reporting Information [Line Items]
Revenue	141,668	292,514
Costs of products sold, exclusive of depreciation and amortization shown below	105,145	254,537
Operating	21,162	15,139
General and administrative	5,622	3,942
Depreciation and amortization	10,143	11,482
Loss (gain) on disposal of long-lived assets, net	152	(34)
Total expenses	142,224	285,066
Earnings from equity method investments	20,864	11,371
Gain on issuance of common units by equity method investee		0
Operating income	20,308	18,819
Other expenses (income), net	10,646	4,663
Income (loss) from continuing operations before income taxes	9,662	14,156
Total assets at March 31, 2015 (excluding intersegment receivables)	1,188,963
SemStream [Member]
Segment Reporting Information [Line Items]
Revenue	0	0
Costs of products sold, exclusive of depreciation and amortization shown below	0	0
Operating	0
General and administrative	3	113
Depreciation and amortization	0	0
Loss (gain) on disposal of long-lived assets, net	0	0
Total expenses	3	113
Earnings from equity method investments	(305)	3,591
Gain on issuance of common units by equity method investee		8,127
Operating income	(308)	11,605
Other expenses (income), net	(9,216)	(1,264)
Income (loss) from continuing operations before income taxes	8,908	12,869
Total assets at March 31, 2015 (excluding intersegment receivables)	135,808
SemCAMS [Member]
Segment Reporting Information [Line Items]
Revenue	29,724	39,283
Costs of products sold, exclusive of depreciation and amortization shown below	132	67
Operating	18,331	23,666
General and administrative	3,376	3,980
Depreciation and amortization	3,066	2,829
Loss (gain) on disposal of long-lived assets, net	0	0
Total expenses	24,905	30,542
Earnings from equity method investments	0	0
Gain on issuance of common units by equity method investee		0
Operating income	4,819	8,741
Other expenses (income), net	3,069	4,155
Income (loss) from continuing operations before income taxes	1,750	4,586
Total assets at March 31, 2015 (excluding intersegment receivables)	275,308
SemGas [Member]
Segment Reporting Information [Line Items]
Revenue	66,257	100,578
Costs of products sold, exclusive of depreciation and amortization shown below	41,269	78,582
Operating	8,046	7,444
General and administrative	2,063	1,972
Depreciation and amortization	7,138	4,969
Loss (gain) on disposal of long-lived assets, net	(1)	4
Total expenses	58,515	92,971
Earnings from equity method investments	0	0
Gain on issuance of common units by equity method investee		0
Operating income	7,742	7,607
Other expenses (income), net	2,851	1,689
Income (loss) from continuing operations before income taxes	4,891	5,918
Total assets at March 31, 2015 (excluding intersegment receivables)	686,665
SemLogistics [Member]
Segment Reporting Information [Line Items]
Revenue	5,152	4,790
Costs of products sold, exclusive of depreciation and amortization shown below	0	350
Operating	2,614	2,080
General and administrative	1,677	1,422
Depreciation and amortization	2,040	2,495
Loss (gain) on disposal of long-lived assets, net	0	0
Total expenses	6,331	6,347
Earnings from equity method investments	0	0
Gain on issuance of common units by equity method investee		0
Operating income	(1,179)	(1,557)
Other expenses (income), net	1,116	251
Income (loss) from continuing operations before income taxes	(2,295)	(1,808)
Total assets at March 31, 2015 (excluding intersegment receivables)	143,778
SemMexico [Member]
Segment Reporting Information [Line Items]
Revenue	61,490	71,610
Costs of products sold, exclusive of depreciation and amortization shown below	51,507	61,469
Operating	2,937	2,449
General and administrative	1,942	2,751
Depreciation and amortization	1,053	1,427
Loss (gain) on disposal of long-lived assets, net	(19)	(28)
Total expenses	57,420	68,068
Earnings from equity method investments	0	0
Gain on issuance of common units by equity method investee		0
Operating income	4,070	3,542
Other expenses (income), net	69	(45)
Income (loss) from continuing operations before income taxes	4,001	3,587
Total assets at March 31, 2015 (excluding intersegment receivables)	98,546
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenue	(5,981)	(9,892)
Costs of products sold, exclusive of depreciation and amortization shown below	(5,981)	(9,892)
Operating		0
General and administrative	17,627	4,556
Depreciation and amortization	294	435
Loss (gain) on disposal of long-lived assets, net	926	0
Total expenses	12,866	(4,901)
Earnings from equity method investments	0	0
Gain on issuance of common units by equity method investee		0
Operating income	(18,847)	(4,991)
Other expenses (income), net	(2,448)	(1,952)
Income (loss) from continuing operations before income taxes	(16,399)	(3,039)
Total assets at March 31, 2015 (excluding intersegment receivables)	332,472
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue	298,310	498,883
Operating Segments [Member] \| Crude [Member]
Segment Reporting Information [Line Items]
Revenue	141,668	292,514
Operating Segments [Member] \| SemStream [Member]
Segment Reporting Information [Line Items]
Revenue	0	0
Operating Segments [Member] \| SemCAMS [Member]
Segment Reporting Information [Line Items]
Revenue	29,724	39,283
Operating Segments [Member] \| SemGas [Member]
Segment Reporting Information [Line Items]
Revenue	60,276	90,686
Operating Segments [Member] \| SemLogistics [Member]
Segment Reporting Information [Line Items]
Revenue	5,152	4,790
Operating Segments [Member] \| SemMexico [Member]
Segment Reporting Information [Line Items]
Revenue	61,490	71,610
Operating Segments [Member] \| Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenue	0	0
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue	0	0
Intersegment Eliminations [Member] \| Crude [Member]
Segment Reporting Information [Line Items]
Revenue	0	0
Intersegment Eliminations [Member] \| SemStream [Member]
Segment Reporting Information [Line Items]
Revenue	0	0
Intersegment Eliminations [Member] \| SemCAMS [Member]
Segment Reporting Information [Line Items]
Revenue	0	0
Intersegment Eliminations [Member] \| SemGas [Member]
Segment Reporting Information [Line Items]
Revenue	5,981	9,892
Intersegment Eliminations [Member] \| SemLogistics [Member]
Segment Reporting Information [Line Items]
Revenue	0	0
Intersegment Eliminations [Member] \| SemMexico [Member]
Segment Reporting Information [Line Items]
Revenue	0	0
Intersegment Eliminations [Member] \| Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenue	$ (5,981)	$ (9,892)

Gain (loss) on issuance of equity by equity method investee

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Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Total costs related to goods produced and sold during the reporting period.

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Total costs of sales and operating expenses for the period.

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- Definition

The current period expense charged against earnings on long-lived, physical assets not used in production, and which are not intended for resale, to allocate or recognize the cost of such assets over their useful lives; or to record the reduction in book value of an intangible asset over the benefit period of such asset; or to reflect consumption during the period of an asset that is not used in production.

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- Definition

Amount of gain (loss) on sale or disposal of property, plant and equipment assets, excluding oil and gas property and timber property.

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The aggregate total of expenses of managing and administering the affairs of an entity, including affiliates of the reporting entity, which are not directly or indirectly associated with the manufacture, sale or creation of a product or product line.

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This element represents the income or loss from continuing operations attributable to the economic entity which may also be defined as revenue less expenses from ongoing operations, after income or loss from equity method investments, but before income taxes, extraordinary items, and noncontrolling interest.

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This item represents the entity's proportionate share for the period of the net income (loss) of its investee (such as unconsolidated subsidiaries and joint ventures) to which the equity method of accounting is applied. This item includes income or expense related to stock-based compensation based on the investor's grant of stock to employees of an equity method investee.

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The aggregate amount of income or expense from ancillary business-related activities (that is to say, excluding major activities considered part of the normal operations of the business).

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Generally recurring costs associated with normal operations except for the portion of these expenses which can be clearly related to production and included in cost of sales or services. Excludes Selling, General and Administrative Expense.

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The net result for the period of deducting operating expenses from operating revenues.

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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