For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=84177426&loc=d3e6351-108592

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13531-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=84177426&loc=d3e6404-108592

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13537-108611

Name:	us-gaap_ConcentrationRiskPercentage1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Fair value measurements (Percentages of Total Commodity Sales Excluding Effects of Hedging Activities (Details) - Customer Concentration Risk - Commodity Sales	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Valero Energy Corporation
Concentration Risk [Line Items]
Percentage of sales to significant purchaser	13.30%
Valero Energy Corporation \| Predecessor
Concentration Risk [Line Items]
Percentage of sales to significant purchaser		15.60%	20.70%
Coffeyville Resources LLC
Concentration Risk [Line Items]
Percentage of sales to significant purchaser	20.90%
Coffeyville Resources LLC \| Predecessor
Concentration Risk [Line Items]
Percentage of sales to significant purchaser		19.30%	14.50%
Phillips 66 Company
Concentration Risk [Line Items]
Percentage of sales to significant purchaser	14.60%
Phillips 66 Company \| Predecessor
Concentration Risk [Line Items]
Percentage of sales to significant purchaser		15.10%	11.80%