Notes Payable (Credit Facility and Construction Loan Textuals) (Details) (Line of Credit [Member], USD $)	12 Months Ended
	Dec. 31, 2014	May 28, 2014	Feb. 28, 2012
Line of Credit Facility [Line Items]
Previous borrowing capacity under the credit facility			$ 350,000,000
Line of Credit Facility, Increase in Borrowing Capacity		150,000,000
Line of Credit Facility, Current Borrowing Capacity		500,000,000
Debt Instrument, Previous Maturity Date	Feb. 28, 2016
Debt Instrument, Maturity Date	May 28, 2019
Line of Credit Facility, Expansion Amount		250,000,000
Line of credit maximum borrowing capacity	359,800,000	750,000,000
Unencumbered interest coverage ratio	2.00
Minimum consolidated fixed charge coverage ratio	1.50
Leverage ratio, upper limit (percent)	60.00%
Shareholders' Equity, Minimum	$ 1,000,000,000.00
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
Debt Instrument, Basis Spread on Variable Rate	0.50%
LIBOR [Member]
Line of Credit Facility [Line Items]
Adjusted interest rate for construction loan	LIBOR
Variable rate basis	LIBOR
Debt Instrument, Basis Spread on Variable Rate	1.10%
Debt Instrument, Base Rate Spread on Variable Rate	1.00%