Segment Information (Assets for Reportable Segments) (Details) - Parent Company [Member] - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 11,491,919	$ 11,604,491
Large Market Same Store
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	4,003,859	4,126,885
Secondary Market Same Store
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	1,718,237	1,768,183
Non Same Store And Other
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	5,570,003	5,479,780
Corporate assets
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 199,820	$ 229,643