Debt and Capital Markets (Schedule of Long-term Debt Instruments) (Details) (USD $)	3 Months Ended								3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Mar. 26, 2014 Term loan payable, due July 23, 2018 [Member]	Dec. 31, 2013 Term loan payable, due July 23, 2018 [Member]	Mar. 31, 2014 Line of Credit [Member]	Mar. 26, 2014 Line of Credit [Member]	Dec. 31, 2013 Line of Credit [Member]	Mar. 31, 2014 direct share purchase plan [Member]
Debt Instrument [Line Items]
Gain on early extinguishment of debt	$ 0	$ 4,539,000
Line of Credit Facility, Current Borrowing Capacity				275,000,000	265,000,000		535,000,000	475,000,000
Debt	1,482,608,000		1,475,336,000
Line of Credit Facility, Amount Outstanding						0
Line of Credit Facility, Remaining Borrowing Capacity						535,000,000
Common Shares, shares issued	55,227,234		53,361,261						1,563,709
Net proceeds from issuance of common shares	$ 79,579,000	$ 84,000							$ 79,500,000