Summary Of Significant Accounting Policies (Recent Accounting Pronouncements) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) lease property	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jan. 01, 2019 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect on Retained Earnings, Net of Tax	$ (6,028)	$ 0
Net Cash Provided by (Used in) Operating Activities	516,688	458,828	$ 427,672
Net Cash Provided by (Used in) Investing Activities	$ (192,247)	(837,922)	(590,221)
Number of Properties Subject to Ground Leases | property	14
Capital Leased Assets, Number of Units | lease	4
Capitalized internal leasing and external legal leasing costs	$ 7,500
Real estate taxes paid by tenants to taxing authorities	6,500
Additional cumulative effect
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect on Retained Earnings, Net of Tax	600
Condominium sales
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect on Retained Earnings, Net of Tax	5,400
Cumulative Effect on Retained Earnings, Tax	1,400
Subsequent Event
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
The obligation liability and right of use asset				$ 75,000
Pro Forma | Condominium sales
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Percentage of completion gain	700
Income Tax Expense (Benefit)	$ 200
Restatement Adjustment | Accounting Standards Update 2016-18
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net Cash Provided by (Used in) Operating Activities		458,800	427,700
Net Cash Provided by (Used in) Investing Activities		(837,900)	(590,200)
Previously Reported | Accounting Standards Update 2016-18
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net Cash Provided by (Used in) Operating Activities		423,700	369,000
Net Cash Provided by (Used in) Investing Activities		$ (590,200)	$ (353,800)