Consolidated Statements of Cash Flows - Supplemental Information (Supplemental Information Related to Cash Flows) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Supplemental Cash Flow Elements [Abstract]
Interest paid, net of amounts capitalized	$ 13,775	$ 13,582
Income taxes paid	0	0
Non-Cash Transactions:
Transfer from projects under development to operating properties	212,628	0
Change in accrued property acquisition, development, and tenant expenditures	28,465	411
Common stock dividends declared	27,315	25,135
Cumulative effect of change in accounting principle	22,329	0
Transfer from investment in unconsolidated joint ventures to operating properties	0	68,390
Transfer from operating properties to real estate assets and other assets held for sale	0	44,653
Transfer from operating properties to liabilities of real estate assets held for sale	$ 0	$ (130,691)