Supplemental Cash Flow Disclosure (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Conversion of operating partnership units into common shares - value	$ 8,600		$ 55,700
Conversion of operating partnership units into common shares - shares	1,279		6,080
Depreciation and amortization from continuing operations	$ 114,054,000	$ 114,452,000	$ 115,819,000
Debt retirement		880,500,000	310,200,000
Payment on line of credit	156,000,000	314,500,000	251,000,000
Long-term Debt	1,338,326,000	1,409,889,000
Normal recurring principal payments	2,700,000	2,600,000	3,300,000
Increase/Decrease in accrued expenses and other liabilities	$ (4,500,000)	2,700,000	(11,300,000)
Construction tranche [Member]
Debt Instrument [Line Items]
Normal recurring principal payments		$ 6,300,000	$ 58,600,000