Supplemental Disclosure to Statements of Cash Flows (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Supplemental Cash Flow Information [Abstract]
Write off of fully depreciated/amortized property and deferred costs	$ 28,877	$ 20,672
Write off of depreciated property and deferred costs due to sale	76,533	132,707
Unrealized loss on cash flow hedge	(319)	(1,656)
Changes in accrued development capital expenditures	(10,974)	4,280
Non cash change in investment in unconsolidated joint ventures	$ 0	$ (11,948)