Summary Of Significant Accounting Policies Recently Adopted Accounting Pronouncements (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($) lease property	Sep. 30, 2017 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative impact to accumulated dividends in excess of net income, net of tax	$ (6,028)
Net cash provided by operating activities	364,716	$ 339,471
Net cash used in investing activities	$ (111,773)	(709,400)
Properties subject to ground leases | property	14
Capital leases | lease	4
Capitalized internal leasing and external legal leasing costs	$ 5,300
Condominium sales
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative impact to accumulated dividends in excess of net income, net of tax	5,400
Cumulative impact to accumulated dividends in excess of net income, tax	1,400
Additional cumulative effect
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative impact to accumulated dividends in excess of net income, net of tax	$ 600
Previously Reported | ASU 2016-18
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by operating activities		339,600
Net cash used in investing activities		(708,300)
Restatement Adjustment | ASU 2016-18
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by operating activities		339,500
Net cash used in investing activities		$ (709,400)