Supplemental Disclosure to Statements of Cash Flows (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Supplemental Cash Flow Information [Abstract]
Write-off of fully depreciated/amortized property and deferred costs	$ 44,216	$ 31,322
Write-off of depreciated/amortized property and deferred costs due to sale/demolition	95,277	132,707
Unrealized loss on cash flow hedge	(1,539)	(990)
Changes in accrued development capital expenditures	5,023	7,854
Increase in investments in and advances to unconsolidated joint ventures	$ 0	$ (11,948)