Schedule of Supplemental Information to Statements of Cash Flows (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Supplemental Cash Flow Information [Abstract]
Interest paid, net of capitalized interest	$ 12,976	$ 13,587
Interest capitalized	224	59
Income taxes refunded, net	160	164
Increase in distributions payable on common shares	53	27
Write-off of fully amortized deferred financing costs	0	23
Decrease in accrued capital expenditures	(1,066)	(1,841)
Grant of nonvested shares and awards to employees and executives, net	3,686	3,762
Issuance of common shares for Board of Trustees compensation	691	602
Investment in properties (after credits at closing)	(445,734)	0
Other assets	(1,897)	0
Liabilities	8,474	0
Acquisition of properties	$ (439,157)	$ 0