Organization and Operation (Details)	Dec. 31, 2013 sqft item
Organization and Operation
Properties owned	3,896
Number of U.S. states where properties are owned	49
Leasable square feet	62,600,000

The number of states the entity operates in as of the balance sheet date.

No definition available.

Name:	us-gaap_NumberOfStatesInWhichEntityOperates
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant