Summary of Significant Accounting Policies - Organization and Principles of Consolidation (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) retail_shopping_center property shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($)
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Concentration Risk, Percentage	18.00%
Operations Commenced Date	Dec. 31, 1993
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2017
Parent Company, Ownership Percentage of Outstanding Common Partnership Units of Operating Partnership	99.80%	99.90%
General Partners' Capital Account, Units Outstanding | shares	171,364,908	104,497,000
Partners' Capital Account, Units | shares	171,714,810	104,651,000
Maximum Period Of TIme In Which Company Capitalizes Interest Costs	12 months
Tax Basis of Investments, Unrealized Appreciation (Depreciation), Net	$ 2,800,000,000	$ 190,300,000
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount	(9,737,000)	0	$ 0
Parent Company [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Restricted Cash and Cash Equivalents	$ 4,011,000	4,623,000
Conversion of Stock, Conversion Ratio	0.45
Stock Issued During Period, Shares, Acquisitions | shares	65,500,000
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount	$ 9,737,000
Partnership Interest [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Restricted Cash and Cash Equivalents	$ 4,011,000	$ 4,623,000
Wholly Owned Properties [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of Real Estate Properties | property	311
Unconsolidated Properties [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of Real Estate Properties | property	115
Partially Owned Properties [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of Real Estate Properties | retail_shopping_center	126
Consolidated Properties [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of Real Estate Properties | retail_shopping_center	11
Minimum [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Equity Method Investment, Accretion Period	10 years
Maximum [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Concentration Risk, Percentage	5.00%
Equity Method Investment, Accretion Period	40 years
Building and Improvements [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Property, Plant and Equipment, Useful Life	40 years
Tenant Improvements [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Property, Plant and Equipment, Useful Life	10 years
Furniture and Fixtures [Member] | Minimum [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Furniture and Fixtures [Member] | Maximum [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Property, Plant and Equipment, Useful Life	7 years