Summary Of Significant Accounting Policies Recently Adopted Accounting Pronouncements (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($) lease property	Jun. 30, 2017 USD ($)
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	263,111	$ 238,660
Net cash used in investing activities	$ (78,695)	(386,699)
Properties subject to ground leases | property	14
Capital leases | lease	4
Capitalized internal leasing and external legal leasing costs	$ 3,600
ASU 2016-18 | Before adoption of standard
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by operating activities		241,800
Net cash used in investing activities		(390,000)
ASU 2016-18 | After adoption of standard
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by operating activities		238,700
Net cash used in investing activities		$ (386,700)
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