Cash flow information (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Cash flow information [Abstract]
Interest, net of amount capitalized	$ 41,440	$ 35,893
Income taxes paid (refunded), net	(2,649)	2,418
Property, plant and equipment additions in accounts payable	$ 77,073	$ 76,505