Equity (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
SemGroup owners' equity:
Beginning Balance	$ 1,021,528
Net income (loss) attributable to SemGroup	48,566	2,110
Other comprehensive income (loss), net of income taxes	(5,058)	12,755
Distributions to noncontrolling interests	(3,624)
Noncontrolling interest, increase from equity issuance	57,886
Sale of interest in equity investment to related party	(33,716)
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition	1,183
Issuance of common stock under compensation plans	0
Repurchase of common stock	(371)
Ending Balance	1,086,394
Common Stock [Member]
SemGroup owners' equity:
Beginning Balance	420
Net income (loss) attributable to SemGroup	0
Other comprehensive income (loss), net of income taxes	0
Distributions to noncontrolling interests	0
Noncontrolling interest, increase from equity issuance	0
Sale of interest in equity investment to related party	0
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition	0
Issuance of common stock under compensation plans	1
Repurchase of common stock	0
Ending Balance	421
Additional Paid-In Capital [Member]
SemGroup owners' equity:
Beginning Balance	1,039,189
Net income (loss) attributable to SemGroup	0
Other comprehensive income (loss), net of income taxes	0
Distributions to noncontrolling interests	0
Noncontrolling interest, increase from equity issuance	0
Sale of interest in equity investment to related party	56,800
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition	1,040
Issuance of common stock under compensation plans	(1)
Repurchase of common stock	0
Ending Balance	1,097,028
Treasury Stock [Member]
SemGroup owners' equity:
Beginning Balance	(242)
Net income (loss) attributable to SemGroup	0
Other comprehensive income (loss), net of income taxes	0
Distributions to noncontrolling interests	0
Noncontrolling interest, increase from equity issuance	0
Sale of interest in equity investment to related party	0
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition	0
Issuance of common stock under compensation plans	0
Repurchase of common stock	(371)
Ending Balance	(613)
Accumulated Deficit [Member]
SemGroup owners' equity:
Beginning Balance	(145,674)
Net income (loss) attributable to SemGroup	43,423
Other comprehensive income (loss), net of income taxes	0
Distributions to noncontrolling interests	0
Noncontrolling interest, increase from equity issuance	0
Sale of interest in equity investment to related party	0
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition	0
Issuance of common stock under compensation plans	0
Repurchase of common stock	0
Ending Balance	(102,251)
Accumulated Other Comprehensive Income (Loss) [Member]
SemGroup owners' equity:
Beginning Balance	(1,299)
Net income (loss) attributable to SemGroup	0
Other comprehensive income (loss), net of income taxes	(5,058)
Distributions to noncontrolling interests	0
Noncontrolling interest, increase from equity issuance	0
Sale of interest in equity investment to related party	0
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition	0
Issuance of common stock under compensation plans	0
Repurchase of common stock	0
Ending Balance	(6,357)
Noncontrolling Interest [Member]
SemGroup owners' equity:
Beginning Balance	129,134
Net income (loss) attributable to SemGroup	5,143
Other comprehensive income (loss), net of income taxes	0
Distributions to noncontrolling interests	(3,624)
Noncontrolling interest, increase from equity issuance	57,886
Sale of interest in equity investment to related party	(90,516)
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition	143
Issuance of common stock under compensation plans	0
Repurchase of common stock	0
Ending Balance	$ 98,166