Notes Payable (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Interest incurred and expensed on the notes payable
Loss on derivatives	$ 406,000	$ 2,655,000
Accretion of Senior Notes	1,058,000	1,062,000	996,000
Amortization of deferred financing fees	3,690,000	3,138,000	1,457,000
Write-off of deferred financing fees	3,000	21,000	1,462,000
Total interest incurred and expensed on the notes payable	76,821,000	74,195,000	58,931,000
Aggregate future principal maturities and amortization of notes payable
Total	1,363,392,000	1,418,025,000
Notes payable.
Interest incurred and expensed on the notes payable
Interest expense	71,664,000	67,319,000	54,839,000
Loss on derivatives	406,000	2,655,000
Accretion of Senior Notes	1,058,000	1,062,000	996,000
Amortization of deferred financing fees	3,690,000	3,138,000	1,457,000
Write-off of deferred financing fees	3,000	21,000	1,462,000
Loan penalties and fees			177,000
Total interest incurred and expensed on the notes payable	76,821,000	74,195,000	58,931,000
Aggregate future principal maturities and amortization of notes payable
2013	76,726,000
2014	22,321,000
2015	158,217,000
2016	423,586,000
2017	250,223,000
Thereafter	432,319,000
Total	$ 1,363,392,000