Supplemental Disclosure to Statements of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Supplemental Disclosure to Statements of Cash Flows [Abstract]
Write-off of fully depreciated/amortized property and deferred costs	$ 42,339	$ 38,131	$ 22,269
Write-off of depreciated property and deferred costs due to sale/demolition	252,017	173,083	202,695
Write-off of preferred units costs due to redemption	0	0	1,214
Assumption of mortgage loans in connection with the acquisition of properties	0	0	229,751
Increase in investments in and advances to unconsolidated joint ventures due to disposition/development activity	0	(11,948)	0
Changes in accrued development capital expenditures	11,964	6,264	17,053
Unrealized (loss) gain on cash flow hedge	$ (488)	$ (3,419)	$ 1,584