Equity - Additional Information (Details) $ / shares in Units, $ in Thousands	1 Months Ended	9 Months Ended
	Jul. 31, 2015 USD ($) shares	Sep. 30, 2016 USD ($) $ / shares shares	Sep. 30, 2015 USD ($) $ / shares shares	Dec. 31, 2015 USD ($)
Equity [Line Items]
Payments to Acquire Real Estate		$ 0	$ 4,022
Proceeds from issuance of common shares		$ 2,686	$ 17,312
Authorized amount (in shares) | shares	10,000,000
Treasury stock acquired (in shares) | shares		1,184,113	1,306,300
Treasury stock acquired, average cost (in dollars per share) | $ / shares		$ 7.56	$ 8.42
Gains and losses on cash flow hedges		$ (4,883)		$ (1,939)
OP unit equivalent in common shares		1.13
Partners' capital account (in units) | shares		3,387,000
Direct Share Purchase Plan [Member]
Equity [Line Items]
Common shares issued during period (in shares) | shares		577,823	1,845,617
Proceeds from issuance of common shares		$ 4,115	$ 17,415
Philadelphia, Pennsylvania [Member]
Equity [Line Items]
Payments to Acquire Real Estate	$ 4,022
Real Estate, Ownership	100.00%