Consolidated Statements of Cash Flows - Supplemental Information (Supplemental Information Related to Cash Flows) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Supplemental Cash Flow Elements [Abstract]
Interest paid, net of amounts capitalized	$ 19,283	$ 22,721
Non-Cash Transactions:
Transfer from projects under development to operating properties	212,628	58,928
Common stock dividends declared and accrued	27,326	25,212
Change in accrued property acquisition, development, and tenant expenditures	24,121	(1,110)
Cumulative effect of change in accounting principle	22,329	0
Transfer from investment in unconsolidated joint ventures to projects under development	7,025	0
Transfer from investment in unconsolidated joint ventures to operating properties	$ 0	$ 68,390