Cash flow information (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Supplemental Cash Flow Information [Abstract]
Interest, net of amount capitalized	$ 39,441	$ 41,440
Income taxes paid (refunded), net	39,984	(2,649)
Property, plant and equipment additions in accounts payable	$ 95,833	$ 77,073