Supplemental Disclosure to Statements of Cash Flows (Details) - USD ($)	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Supplemental Cash Flow Information [Abstract]
Write-off of fully depreciated/amortized property and deferred costs	$ 26,349,000	$ 44,216,000
Write-off of depreciated/amortized property and deferred costs due to sale/demolition	34,513,000	95,277,000
Write-off of costs related to early debt extinguishment	109,000	0
Conversion of Stock [Line Items]
Unrealized loss on cash flow hedge	(1,132,000)	(1,539,000)
Changes in accrued development capital expenditures	(7,522,000)	5,023,000
Capitalized equity-based compensation in development in progress	980,000	0
Common units into common shares [Member]
Conversion of Stock [Line Items]
Redemption of noncontrolling interests - common units	$ 132,000	$ 224,000