Quarterly Financial Data (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Data [Abstract]
Total revenues	$ 547,237	$ 594,235	$ 482,224	$ 498,883	$ 457,328	$ 357,748	$ 324,244	$ 287,696	$ 2,122,579	$ 1,427,016	$ 1,237,497
Loss (gain) on disposal or impairment of long-lived assets, net	11,959	1,376	19,315	(58)	(109)	408	(376)	(162)	32,592	(239)	(3,531)
Other operating costs and expenses	530,150	575,936	471,863	478,264	448,796	344,979	312,103	282,813	2,056,213	1,388,691
Total expenses	542,109	577,312	491,178	478,206	448,687	345,387	311,727	282,651	2,088,805	1,388,452	1,216,182
Earnings from equity method investments	15,827	14,223	19,187	14,962	12,788	7,483	14,861	17,345	64,199	52,477	36,036
Gain on issuance of common units by equity method investee	2,121	18,772	0	8,127	26,873	0	0	0	29,020	26,873	0
Operating income	23,076	49,918	10,233	43,766	48,302	19,844	27,378	22,390	126,993	117,914	57,351
Other expenses, net	(2,196)	(6,368)	29,489	7,497	17,646	13,294	10,613	27,862	28,422	69,415	30,471
Income (loss) from continuing operations before income taxes	25,272	56,286	(19,256)	36,269	30,656	6,550	16,765	(5,472)	98,571	48,499	26,880
Income tax expense (benefit)	12,569	24,090	(6,672)	16,526	24,051	3,413	9,288	(54,006)	46,513	(17,254)	(2,078)
Income (loss) from continuing operations	12,703	32,196	(12,584)	19,743	6,605	3,137	7,477	48,534	52,058	65,753	28,958
Income (loss) from discontinued operations, net of income taxes	4	0	0	(5)	(6)	(2)	35	32	(1)	59	2,939
Net income (loss)	12,707	32,196	(12,584)	19,738	6,599	3,135	7,512	48,566	52,057	65,812	31,897
Less: net income attributable to noncontrolling interests	4,633	6,934	5,025	6,150	3,319	5,054	3,943	5,143	22,817	17,710	9,797
Net income (loss) attributable to SemGroup	$ 8,074	$ 25,262	$ (17,609)	$ 13,588	$ 3,280	$ (1,919)	$ 3,569	$ 43,423	$ 29,240	$ 48,102	$ 22,100
Basic earnings (loss) per share, net	$ 0.19	$ 0.59	$ (0.41)	$ 0.32	$ 0.08	$ (0.05)	$ 0.08	$ 1.03	$ 0.69	$ 1.14	$ 0.53
Earnings Per Share, Diluted	$ 0.18	$ 0.59	$ (0.41)	$ 0.29	$ 0.08	$ (0.05)	$ 0.08	$ 1.03	$ 0.68	$ 1.13	$ 0.52