Supplemental Disclosure to Statements of Cash Flows (Details) - USD ($)	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Supplemental Cash Flow Information [Abstract]
Write-off of fully depreciated/amortized property and deferred costs	$ 19,002,000	$ 28,877,000
Write-off of depreciated/amortized property and deferred costs due to sale/demolition	33,857,000	76,533,000
Unrealized loss on cash flow hedge	(1,795,000)	(319,000)
Changes in accrued development capital expenditures	2,383,000	(10,974,000)
Capitalized equity-based compensation in development in progress	$ 808,000	$ 0