Segment Information (Assets for Reportable Segments) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 2,751,068	$ 2,530,468
Large Market Same Store
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	1,108,827	1,017,015
Secondary Market Same Store
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	654,315	668,109
Non Same Store And Other
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	949,398	760,132
Corporate assets
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 38,528	$ 85,212