Basis of presentation (Details)	9 Months Ended
Sep. 30, 2012
Basis of presentation
Percentage of ownership interest criteria	100.00%
Land improvements
Property, plant and equipment depreciated on a straight-line basis using an estimated life
Estimated life	20 years
Buildings and building improvements \| Maximum
Property, plant and equipment depreciated on a straight-line basis using an estimated life
Estimated life	40 years

Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

No definition available.

Name:	us-gaap_PropertyPlantAndEquipmentUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration