Notes Payable (Credit Facility and Construction Loan Textuals) (Details) - Line of Credit [Member]	12 Months Ended
	Dec. 31, 2015 USD ($)
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 500,000,000
Debt Instrument, Maturity Date	May 28, 2019
Line of Credit Facility, Remaining Borrowing Capacity	$ 750,000,000
Line of credit maximum borrowing capacity	$ 407,000,000
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]
Debt Instrument, Description of Variable Rate Basis	prime rate
Federal funds rate [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Description of 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
Debt Instrument, Description of Variable Rate Basis	LIBOR
Debt Instrument, Basis Spread on Variable Rate	1.10%
Debt Instrument, Base Rate Spread on Variable Rate	1.00%