Rose Rock Midstream, L.P. - Summarized balance sheet information (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Summarized Balance Sheet Information
Other current assets	$ 15,770us-gaap_OtherAssetsCurrent	$ 20,017us-gaap_OtherAssetsCurrent
Property, plant and equipment, net	1,303,781us-gaap_PropertyPlantAndEquipmentNet	1,256,825us-gaap_PropertyPlantAndEquipmentNet
Equity method investment	561,463us-gaap_EquityMethodInvestments	577,920us-gaap_EquityMethodInvestments
Goodwill	58,159us-gaap_Goodwill	58,326us-gaap_Goodwill
Other noncurrent assets, net	56,805us-gaap_OtherAssetsNoncurrent	44,386us-gaap_OtherAssetsNoncurrent
Total assets	2,861,540us-gaap_Assets	2,589,802us-gaap_Assets
Current liabilities	349,388us-gaap_LiabilitiesCurrent	391,662us-gaap_LiabilitiesCurrent
Long-term debt	1,027,072	767,092
Total liabilities and owners’ equity	2,861,540	2,589,802
Rose Rock Midstream, L.P. [Member]
Summarized Balance Sheet Information
Cash	13,323	3,625
Other current assets	261,942	271,144
Property, plant and equipment, net	405,283	396,066
Equity method investment	425,655	269,635
Goodwill	36,116	36,116
Other noncurrent assets, net	28,847	29,677
Total assets	1,171,166	1,006,263
Current liabilities	227,607	265,682
Long-term debt	661,072	432,092
Partners’ capital attributable to SemGroup	179,280	238,560
Partners’ capital attributable to noncontrolling interests	103,207	69,929
Total liabilities and owners’ equity	$ 1,171,166	$ 1,006,263

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