Basis of presentation (Details)	6 Months Ended
Jun. 30, 2012 Y
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 (in years)	20
Buildings and building improvements \| Maximum
Property, plant and equipment depreciated on a straight-line basis using an estimated life
Estimated life (in years)	40

The average useful life of long-lived, physical assets used in the normal conduct of business and not intended for resale. Examples include land, buildings, machinery and equipment, and other types of furniture and equipment including, but not limited to, office equipment, furniture and fixtures, and computer equipment and software.

No definition available.

Name:	us-gaap_PropertyPlantAndEquipmentUsefulLifeAverage
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	duration