Supplemental Cash Flow Disclosure (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Conversion of operating partnership units into common shares - value	$ 0	$ 55,700	$ 23,000
Conversion of operating partnership units into common shares - shares		6,080	3,839
Depreciation and amortization from continuing operations	114,452,000	$ 115,819,000	$ 119,624,000
Depreciation and amortization from discontinued operations	0	0	4,923,000
Total depreciation and amortization expense	114,452,000	115,819,000	124,547,000
Debt retirement	880,500,000	310,200,000
Payment on line of credit	314,500,000	251,000,000	132,000,000
Long-term Debt	1,427,954,000	1,585,867,000
Normal recurring principal payments	2,600,000	3,300,000	4,900,000
Increase/Decrease in accrued expenses and other liabilities	2,700,000	(11,300,000)	$ 11,000,000
Construction tranche [Member]
Debt Instrument [Line Items]
Debt retirement	$ 6,300,000	$ 58,600,000