Supplemental Cash Flow Disclosure (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Supplemental Cash Flow Elements [Abstract]
Conversion of operating partnership units into common shares - value	$ 45,000	$ 97,000	$ 0
Conversion of operating partnership units into common shares - shares	11,473	15,947
Units received as payment for amounts owed to us by a unit holder	3,571
Depreciation and amortization from continuing operations	123,879,000	118,232,000	116,439,000
Depreciation and amortization from discontinued operations	5,607,000	20,660,000	31,224,000
Total depreciation and amortization expense	129,486,000	138,892,000	147,663,000
Debt retirement	828,000,000	983,400,000
Payment on line of credit	192,000,000	145,000,000
Normal recurring principal payments	$ 23,300,000	$ 7,400,000