Cash flow information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Supplemental Cash Flow Information [Abstract]
Interest, net of amount capitalized	$ 20,850	$ 21,857
Income taxes paid (refunded), net	9,435	(7,246)
Property, plant and equipment additions in accounts payable	$ 65,736	$ 92,236