Business exit costs (Details 4) - Discontinued operations, held-for-sale or disposed of by sale [Member] - Exploration and production [Member] - USD ($)	3 Months Ended				9 Months Ended	12 Months Ended	15 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2016
Other restructuring [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Business exit costs	$ 0		$ 300,000		$ 5,600,000	$ 2,500,000	$ 10,500,000
Contract termination [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Business exit costs		$ 3,200,000		$ 3,300,000	$ 900,000