Related Parties (Narrative) (Details) $ in Thousands		1 Months Ended				12 Months Ended
	Feb. 12, 2016 USD ($)	Nov. 30, 2016 USD ($) joint_venture	Oct. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Feb. 29, 2016 USD ($) center	Dec. 31, 2017 USD ($) property center	Dec. 31, 2016 USD ($) property center	Dec. 31, 2015 USD ($) center
Related Party Transaction [Line Items]
Net accounts receivable, related parties						$ 2,000	$ 2,200
Accounts payable and accrued expenses, related parties						400	300
Management fees revenues, related parties						6,200	5,100	$ 4,500
Payments to acquired interest in joint ventures						$ 37,173	$ 52,834	$ 30,053
Number of real estate properties | center						2	2
Assets held by joint venture						$ 4,196,639	$ 4,426,928
Debt held by joint venture						$ 2,006,285
Proceeds from business acquisition					$ 2,500
Number of centers sold					1	18
51% Owned Real Estate joint venture [Member]
Related Party Transaction [Line Items]
Equity interest in joint venture (percent)								51.00%
Number of real estate properties | center								3
Assets held by joint venture								$ 43,700
Debt held by joint venture								$ 72,400
Unconsolidated Real Estate Joint Venture [Member]
Related Party Transaction [Line Items]
Number of centers sold | property						2	5
Consolidated Joint Venture [Member]
Related Party Transaction [Line Items]
Number of real estate join ventures acquired | joint_venture		2
Payments to acquired interest in joint ventures		$ 3,300
Series of Individually Immaterial Business Acquisitions [Member]
Related Party Transaction [Line Items]
Percentage of voting interest acquired				50.00%			50.00%
Equity interest in joint venture				$ 13,500			$ 13,579
Gain recognized on equity interest remeasured to fair value				$ 9,000
Business Combination Achieved in Stages [Member]
Related Party Transaction [Line Items]
Percentage of voting interest acquired	49.00%				49.00%
Equity interest in joint venture	$ 22,514
Gain recognized on equity interest remeasured to fair value	37,383				$ 37,400
Proceeds from business acquisition	$ 2,500
Joint Venture [Member] | Repayments of Notes Payable [Member]
Related Party Transaction [Line Items]
Payable paid due to the unconsolidated joint venture						$ 4,800
Distribution of Nonmonetary Assets to Groups of Stockholders’ in Lieu of Capital Return Cash Distributions [Member] | Unconsolidated Real Estate Joint Venture [Member]
Related Party Transaction [Line Items]
Gain recognized with the remeasurment of a land parcel			$ 1,900