Equity - Equity rollforward (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
SemGroup owners’ equity:
Balance at December 31, 2016	$ 1,445,965
Adoption of ASU 2016-09	483
Net loss	(10,277)	$ (4,893)
Other comprehensive income (loss), net of income taxes	6,033	$ (4,109)
Dividends paid	(29,770)
Unvested dividend equivalent rights	(276)
Non-cash equity compensation	2,717
Issuance of common stock under compensation plans	517
Repurchase of common stock	(1,047)
Balance at March 31, 2017	1,414,345
Common Stock [Member]
SemGroup owners’ equity:
Balance at December 31, 2016	659
Adoption of ASU 2016-09	0
Net loss	0
Other comprehensive income (loss), net of income taxes	0
Dividends paid	0
Unvested dividend equivalent rights	0
Non-cash equity compensation	0
Issuance of common stock under compensation plans	1
Repurchase of common stock	0
Balance at March 31, 2017	660
Additional Paid-In Capital [Member]
SemGroup owners’ equity:
Balance at December 31, 2016	1,561,695
Adoption of ASU 2016-09	(1,650)
Net loss	0
Other comprehensive income (loss), net of income taxes	0
Dividends paid	(29,770)
Unvested dividend equivalent rights	(276)
Non-cash equity compensation	2,717
Issuance of common stock under compensation plans	516
Repurchase of common stock	0
Balance at March 31, 2017	1,533,232
Treasury Stock [Member]
SemGroup owners’ equity:
Balance at December 31, 2016	(6,558)
Adoption of ASU 2016-09	0
Net loss	0
Other comprehensive income (loss), net of income taxes	0
Dividends paid	0
Unvested dividend equivalent rights	0
Non-cash equity compensation	0
Issuance of common stock under compensation plans	0
Repurchase of common stock	(1,047)
Balance at March 31, 2017	(7,605)
Accumulated Deficit [Member]
SemGroup owners’ equity:
Balance at December 31, 2016	(35,917)
Adoption of ASU 2016-09	2,133
Net loss	(10,277)
Other comprehensive income (loss), net of income taxes	0
Dividends paid	0
Unvested dividend equivalent rights	0
Non-cash equity compensation	0
Issuance of common stock under compensation plans	0
Repurchase of common stock	0
Balance at March 31, 2017	(44,061)
Accumulated Other Comprehensive Income (Loss) [Member]
SemGroup owners’ equity:
Balance at December 31, 2016	(73,914)
Adoption of ASU 2016-09	0
Net loss	0
Other comprehensive income (loss), net of income taxes	6,033
Dividends paid	0
Unvested dividend equivalent rights	0
Non-cash equity compensation	0
Issuance of common stock under compensation plans	0
Repurchase of common stock	0
Balance at March 31, 2017	$ (67,881)