Debt and Capital Markets (Schedule of Long-term Debt Instruments) (Details) $ in Thousands		3 Months Ended		9 Months Ended
	Jan. 02, 2018 USD ($) properties	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Apr. 16, 2018 USD ($)	Feb. 28, 2018 USD ($)
Debt Instrument [Line Items]
Extinguishment of Debt, Amount	$ 11,700
Debt Instrument, Interest Rate, Stated Percentage	6.19%
Number of Properties Securing Mortgage Note | properties	1
Costs associated with loan refinancing or payoff		$ 0	$ 1,477	$ 31,958	$ 1,491
Senoir Unsecured Notes Payable, 7.75 Percent, Due July 15, 2020 [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount							$ 250,000
Debt Instrument, Unamortized Premium							$ 28,600
Debt Instrument, Increase, Accrued Interest				2,300
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate							7.75%
Costs associated with loan refinancing or payoff				$ 3,300
Senior Unsecured Notes Payable, 4.95 Percent, Due April 15, 2028 [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount						$ 400,000
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate						4.95%
Senior Unsecured Notes Payable, Percent of Principal Amount Issued						0.98883
Debt Covenant, Debt to Adjusted Total Assets Ratio, Maximum				0.60
Debt Covenant, Secured Debt to Adjusted Total Assets Ratio, Maximum				0.40
Debt Covenant, Debt Service Coverage Ratio, Minimum				1.5
Debt Covenant, Total Unencumbered Assets to Outstanding Unsecured Debt Ratio, Minimum				150.00%