Principles of consolidation and basis of presentation (Details) (USD $)	Mar. 31, 2013 markets properties	Dec. 20, 2012
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of Properties	8
Number of Markets in which Entity Operates	7
Business Acquisition, Share Price		$ 26.50

For an acquired entity, price of a single share of a number of saleable stocks of a company.

No definition available.

Name:	us-gaap_BusinessAcquisitionSharePrice
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant