Summary of Significant Accounting Policies (Capitalization of Costs) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Capitalized Contract Cost [Line Items]
Land	$ 864,990	$ 859,113
Buildings and improvements	15,510,434	15,610,992
Construction in progress and space held for development	1,584,328	1,621,928
Land held for future development	$ 163,081	162,941
As Previously Reported
Capitalized Contract Cost [Line Items]
Land		1,509,764
Buildings and improvements		16,745,210
Construction in progress and space held for development		0
Land held for future development		0
Adjustments
Capitalized Contract Cost [Line Items]
Land		(650,651)
Buildings and improvements		(1,134,218)
Construction in progress and space held for development		1,621,928
Land held for future development		$ 162,941