Summary of Significant Accounting Policies Deferred Leasing and Other Costs (Details)	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Deferred Leasing and Other [Abstract]
Number of Days Past Due	90
Amortization of Intangible Assets	$ 25,000,000	$ 27,200,000	$ 33,700,000
Deferred leasing costs	307,486,000	312,206,000
Acquired lease-related intangible assets	207,057,000	189,927,000
Deferred Leasing Costs and Finite Lived Intangible Assets Acquired, gross	514,543,000	502,133,000
Accumulated amortization - deferred leasing costs	(101,403,000)	(108,177,000)
Accumulated amortization - acquired lease-related intangible assets	(99,341,000)	(101,274,000)
Deferred Costs, Leasing, Net	313,799,000	292,682,000
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	20,918,000
Finite-Lived Intangible Assets, Amortization Expense, Year Two	17,195,000
Finite-Lived Intangible Assets, Amortization Expense, Year Three	14,142,000
Finite-Lived Intangible Assets, Amortization Expense, Year Four	11,272,000
Finite-Lived Intangible Assets, Amortization Expense, Year Five	9,581,000
Finite-Lived Intangible Assets, Amortization Expense, after Year Five	32,134,000
Finite-Lived Intangible Assets, Net	105,242,000
Net Charge to Rental Income Year One	703,000
Net Charge to Rental Income Year Two	639,000
Net Charge to Rental Income Third Year	367,000
Net Charge to Rental Income Year Four	353,000
Net Charge to Rental Income Year Five	353,000
Net Charge to Rental Income After Year Five	59,000
Net Charge to Rental Income	2,474,000
Amortization of above market lease, charge to rental income	$ 777,000	$ 913,000	$ 1,000,000