Summary of significant accounting policies Percentage of assets sold (Details)	Jun. 27, 2016	Feb. 07, 2013
Calumet [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Previous percentage of ownership		50.00%
WBI Energy [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Previous percentage of ownership		50.00%
Percentage of ownership acquired	50.00%