Summary of Significant Accounting Policies - Properties in Development (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Document Fiscal Year Focus	2018
Real Estate and Accumulated Depreciation, Costs Capitalized Subsequent to Acquisition, Carrying Costs	$ 630,202,000
Other Cost and Expense, Operating	1,900,000	$ 1,500,000	$ 1,500,000
Refundable deposits - development
Property, Plant and Equipment [Line Items]
Real Estate and Accumulated Depreciation, Costs Capitalized Subsequent to Acquisition, Carrying Costs	550,000	3,500,000
Parent Company [Member]
Property, Plant and Equipment [Line Items]
Land	4,205,445,000	4,235,032,000
Land Improvements	613,847,000	556,140,000
Buildings	5,088,102,000	4,999,378,000
Building improvements	901,596,000	787,880,000
Development in Process	54,172,000	314,391,000
Real Estate Investment Property, at Cost	$ 10,863,162,000	$ 10,892,821,000