Rose Rock Midstream, L.P. - Summarized balance sheet information (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Summarized Balance Sheet Information
Other current assets	$ 20,560	$ 20,017
Property, plant and equipment, net	1,420,194	1,256,825
Equity method investment	548,831	577,920
Goodwill	58,023	58,326
Other noncurrent assets, net	59,495	44,386
Total assets	2,949,389	2,589,802
Current liabilities	420,145	391,662
Long-term debt	1,044,339	767,092
Total liabilities and owners’ equity	2,949,389	2,589,802
Rose Rock Midstream, L.P. [Member]
Summarized Balance Sheet Information
Cash	68,102	3,625
Other current assets	340,418	271,144
Property, plant and equipment, net	419,458	396,066
Equity method investment	426,058	269,635
Goodwill	36,116	36,116
Other noncurrent assets, net	33,686	29,677
Total assets	1,323,838	1,006,263
Current liabilities	308,116	265,682
Long-term debt	744,339	432,092
Partners’ capital attributable to SemGroup	173,045	238,560
Partners’ capital attributable to noncontrolling interests	98,338	69,929
Total liabilities and owners’ equity	$ 1,323,838	$ 1,006,263