Supplemental Cash Flow Disclosure (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Supplemental Cash Flow Elements [Abstract]
Conversion of operating partnership units into common shares - value	$ 56,000	$ 23,000	$ 45,000
Conversion of operating partnership units into common shares - shares	6,080	3,839	11,473
Units received as payment for amounts owed to us by a unit holder			3,571
Depreciation and amortization from continuing operations	115,819,000	119,624,000	116,384,000
Depreciation and amortization from discontinued operations	0	4,923,000	13,102,000
Total depreciation and amortization expense	115,819,000	124,547,000	129,486,000
Debt retirement	310,200,000		828,000,000
Payment on line of credit	251,000,000	132,000,000	192,000,000
Long-term Debt	1,585,867,000	1,663,226,000
Normal recurring principal payments	3,300,000	4,900,000	23,300,000
Increase/Decrease in accrued expenses and other liabilities	(11,300,000)	11,000,000	(3,100,000)
Libor Plus Four Point Zero Percent Due May 2016 [Member] | Construction tranche [Member]
Supplemental Cash Flow Elements [Abstract]
Long-term Debt	$ 58,562,000	$ 0