Mortgages and Notes Payable (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Debt Instrument [Line Items]
Mortgages and notes payable	$ 1,415,961,000	$ 1,366,004,000
Weighted-average interest rate	5.60%	5.70%
Revolving credit facility, maximum borrowing capacity	300,000,000
Gains (charges) on debt satisfaction from continuing operations	(16,000)	45,000	972,000
Interest Paid, Capitalized	3,062,000	1,792,000	791,000
Scheduled Principal and Balloon Payments on Mortgages and Notes Payable
Line of Credit Facility, Interest Rate Description	During 2012, the Company entered into interest-rate swap agreements to fix LIBOR at a weighted-average rate of 1.42% through January 2019 on the $255,000 of outstanding LIBOR-based borrowings. At December 31, 2012, the Company had $255,000 outstanding under the secured term loan
Minimum [Member]
Debt Instrument [Line Items]
Effective interest rate	3.60%	3.60%
Maximum [Member]
Debt Instrument [Line Items]
Effective interest rate	8.50%	7.80%
Mortgages and Notes Payable [Member]
Scheduled Principal and Balloon Payments on Mortgages and Notes Payable
2013	272,192,000
2014	283,460,000
2015	313,474,000
2016	167,312,000
2017	87,162,000
Thereafter	292,361,000
Long-term debt	1,415,961,000
Line of Credit [Member]
Debt Instrument [Line Items]
Revolving credit facility current borrowing capacity	300,000,000
Debt maturity date	Jan. 31, 2015
Reveolving credit facility increase current borrowing capacity	225,000,000
Revolving credit facility, maximum borrowing capacity	525,000,000
Revolving credit facility amount outstanding	0
Outstanding letters of credit	3,744,000
Secured Term Loan [Member]
Debt Instrument [Line Items]
Debt interest rate percentage	1.42%
Debt instrument amount	255,000,000
Long-term debt, gross	255,000,000
Secured Term Loan 1 [Member]
Debt Instrument [Line Items]
Debt instrument amount	25,000,000
Secured Term Loan 2 [Member]
Debt Instrument [Line Items]
Debt instrument amount	35,551,000
Gains (charges) on debt satisfaction from continuing operations	$ 1,578,000
Condition One [Member] | Secured Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Interest rate stated percentage rate range minimum excluding LIBOR	1.625%
Condition One [Member] | Secured Term Loan [Member]
Debt Instrument [Line Items]
Interest rate stated percentage rate range minimum excluding LIBOR	2.00%
Condition Four [Member] | Secured Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Interest rate stated percentage rate range minimum excluding LIBOR	2.375%
Condition Four [Member] | Secured Term Loan [Member]
Debt Instrument [Line Items]
Interest rate stated percentage rate range minimum excluding LIBOR	2.85%