Supplemental Disclosure to Statements of Cash Flows (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Supplemental Cash Flow Information [Abstract]
Write off of fully depreciated property and deferred costs	$ 20,672	$ 17,784
Write off of depreciated property and deferred costs due to sale	132,707	49,618
Unrealized losses on cash flow hedge, non cash transaction	(1,656)	0
Write-off of preferred units costs due to redemption	0	1,236
Increase in investments in and advances to unconsolidated joint ventures due to disposition activity	(11,948)	0
Changes in accrued development capital expenditures	$ 4,280	$ 794