Notes Payable (Credit Facility Textuals) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Feb. 28, 2012
Line of Credit Facility [Line Items]
Previous borrowing capacity under the credit facility		$ 350
Line of credit maximum borrowing capacity	$ 269.2	$ 500.0
Unencumbered interest coverage ratio	2.00
Minimum consolidated fixed charge coverage ratio	1.40
Possible future minimum consolidated fixed charge coverage ratio	1.50
Leverage ratio, upper limit (percent)	60.00%
Adjusted interest rate for construction loan	LIBOR
Variable rate basis	LIBOR
Basis spread on variable rate (percent)	1.50%
Prime rate [Member]
Line of Credit Facility [Line Items]
Variable rate basis	prime rate
Federal funds rate [Member]
Line of Credit Facility [Line Items]
Variable rate basis	federal funds rate
Basis spread on variable rate (percent)	0.50%
LIBOR [Member]
Line of Credit Facility [Line Items]
Variable rate basis	LIBOR
Basis spread on variable rate (percent)	1.00%