Mortgages and Notes Payable (Details)	3 Months Ended
	Mar. 31, 2016 USD ($) extensions	Mar. 31, 2015 USD ($)	Apr. 19, 2016 USD ($)	Dec. 31, 2015 USD ($)
Debt Instrument [Line Items]
Mortgages and notes payable, net	$ 2,100,937,000			$ 2,491,813,000
Unamortized debt issuance costs	(7,074,000)			(7,801,000)
Repayment of bridge credit facility	107,400,000	$ 91,900,000
Revolving Credit Facility due 2018 [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity on revolving credit facility	$ 475,000,000
Maturity date on revolving credit facility	Jan. 01, 2018
Additional borrowing capacity on revolving credit facility	$ 75,000,000
Number of additional maturity extensions | extensions	2
Term of optional extension	6 months
Facility interest rate basis	LIBOR plus 110 basis points
Interest rate spread (in hundredths)	1.10%
Annual facility fee (in hundredths)	0.20%
Amount outstanding on revolving credit facility	$ 258,000,000
Outstanding letters of credit on revolving credit facility	200,000
Unused borrowing capacity on revolving credit facility	$ 216,800,000
Bridge Term Loan Facility due 2016 [Member]
Debt Instrument [Line Items]
Maturity date on revolving credit facility	Mar. 28, 2016
Repayment of bridge credit facility	$ 350,000,000
Secured indebtedness [Member]
Debt Instrument [Line Items]
Mortgages and notes payable, net	174,475,000			175,281,000
Aggregate undepreciated book value of secured real estate assets	315,800,000
Unsecured indebtedness [Member]
Debt Instrument [Line Items]
Mortgages and notes payable, net	$ 1,933,536,000			$ 2,324,333,000
Subsequent Event [Member] | Revolving Credit Facility due 2018 [Member]
Debt Instrument [Line Items]
Amount outstanding on revolving credit facility			$ 257,000,000
Outstanding letters of credit on revolving credit facility			200,000
Unused borrowing capacity on revolving credit facility			$ 217,800,000