Notes Payable (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Interest incurred and expensed on the notes payable
(Gain) loss on derivatives, net	$ (529,000)	$ (525,000)	$ 406,000
Accretion of Senior Notes		3,000	1,058,000
Total interest incurred and expensed on debt and capital lease obligations	72,315,000	72,239,000	76,821,000
Aggregate future principal maturities and amortization of notes payable
2015	121,328,000
2016	205,802,000
2017	257,405,000
2018	290,852,000
2019	223,880,000
Thereafter	330,025,000
Total notes payable, net	1,429,292,000	1,404,075,000
Notes payable and capital lease obligations
Interest incurred and expensed on the notes payable
Interest expense on debt and capital lease obligations	70,067,000	69,806,000	71,664,000
(Gain) loss on derivatives, net	(529,000)	(525,000)	406,000
Accretion of Senior Notes		3,000	1,058,000
Amortization of deferred financing fees	2,777,000	2,955,000	3,690,000
Write-off of deferred financing fees			3,000
Total interest incurred and expensed on debt and capital lease obligations	$ 72,315,000	$ 72,239,000	$ 76,821,000