Debt and Capital Markets (Schedule of Long-term Debt Instruments) (Details) (USD $)	0 Months Ended	9 Months Ended										9 Months Ended	0 Months Ended			0 Months Ended
	Sep. 23, 2014	Sep. 30, 2014	Sep. 30, 2013	Sep. 23, 2014	Dec. 31, 2013	Sep. 19, 2014 Term loan payable, due July 23, 2018 [Member]	Mar. 26, 2014 Term loan payable, due July 23, 2018 [Member]	Dec. 31, 2013 Term loan payable, due July 23, 2018 [Member]	Sep. 30, 2014 Line of Credit [Member]	Mar. 26, 2014 Line of Credit [Member]	Dec. 31, 2013 Line of Credit [Member]	Sep. 30, 2014 direct share purchase plan [Member]	Apr. 21, 2014 immaterial business acquisition [Member] properties	Apr. 21, 2014 immaterial business acquisition [Member] Note, due April 21, 2016 [Member] Notes Payable, Other Payables [Member]	Apr. 21, 2014 immaterial business acquisition [Member] Note, due April 21, 2016 [Member] Notes Payable, Other Payables [Member]	Apr. 21, 2014 immaterial business acquisition [Member] Mortgage note, due July 6, 2017 [Member] Mortgages [Member]	Apr. 21, 2014 immaterial business acquisition [Member] Mortgage note, due July 6, 2017 [Member] Mortgages [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity						$ 285,000,000	$ 275,000,000	$ 265,000,000		$ 535,000,000	$ 475,000,000
Debt		1,621,211,000			1,475,336,000
Line of Credit Facility, Amount Outstanding									34,000,000
Line of Credit Facility, Remaining Borrowing Capacity									501,000,000
Common Shares, shares issued		58,941,290		3,680,000	53,361,261							1,563,709
Net proceeds from issuance of common shares	184,200,000	264,008,000	43,659,000									79,500,000
Acquisition of real estate in exchange for assumption of debt at fair value		101,441,000	19,710,000											1,900,000		90,300,000
Number of properties acquired (in properties)													11
Debt Instrument, Periodic Payment														12,000		635,000
Debt Instrument Final Principal Payment Due on Maturity																85,100,000
Notes Payable, Fair Value Disclosure																	$ 99,600,000
Estimated Current Market Rate Used As Discount Factor To Determine Fair Value of Notes																0.00%
Debt Instrument, Interest Rate, Stated Percentage															2.50%