Common Share Capitalization (Narrative) (Details) (USD $)	0 Months Ended	2 Months Ended	3 Months Ended				9 Months Ended
	Aug. 04, 2011	Sep. 30, 2011	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013 Dividend		Sep. 30, 2012 Dividend		Dec. 31, 2012
Common Stock Capitalization [Line Items]
Common Shares Issued And Outstanding Upon Conversion of All Convertible Securities			26,031,717				26,031,717
Shareholders Equity Per Share Upon Conversion Of All Convertible Units (in usd per share)			$ 24.19				$ 24.19
Common Shares Issued And Outstanding Upon Conversion Of All LTIP Units											20,767,565
Shareholders' equity per share upon conversion of LTIPs (in usd per share)					$ 23.88				$ 23.88		$ 24.38
Dividends (in usd per share)			$ 0.77		$ 0.70		$ 3.06		$ 1.80
Number of Dividends Authorized							3		3
Dividend Amount			$ 20,040,000	[1]	$ 14,244,000	[1]	$ 72,016,000	[1],[2]	$ 32,766,000	[1],[2]
Aggregate cost of shares repurchase	10,000,000
Shares repurchased		217,619
Aggregate cost of shares repurchased		$ 4,500,000
Average price per share repurchased (in usd per share)		$ 20.59

[1] The Company pays quarterly dividends in arrears, so a portion of the dividends paid in each calendar year relate to the prior year's earnings.

[2] For the nine month periods ended September 30, 2013 and 2012, dividends totaling $3.06 and $1.80, respectively, per common share and convertible unit outstanding were declared and paid.