Rose Rock Midstream, L.P. - Summarized balance sheet information (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Summarized Balance Sheet Information
Other current assets	$ 20,401	$ 20,017
Property, plant and equipment, net	1,474,947	1,256,825
Equity method investment	547,448	577,920
Goodwill	57,592	58,326
Other noncurrent assets, net	61,500	44,386
Total assets	2,877,568	2,589,802
Current liabilities	378,170	391,662
Long-term debt	1,044,468	767,092
Total liabilities and owners’ equity	2,877,568	2,589,802
Rose Rock Midstream, L.P. [Member]
Summarized Balance Sheet Information
Cash	44,011	3,625
Other current assets	304,634	271,144
Property, plant and equipment, net	425,820	396,066
Equity method investment	430,168	269,635
Goodwill	36,116	36,116
Other noncurrent assets, net	32,746	29,677
Total assets	1,273,495	1,006,263
Current liabilities	270,452	265,682
Long-term debt	744,468	432,092
Partners’ capital attributable to SemGroup	165,735	238,560
Partners’ capital attributable to noncontrolling interests	92,840	69,929
Total liabilities and owners’ equity	$ 1,273,495	$ 1,006,263