Common Share Capitalization (Narrative) (Details) (USD $)	0 Months Ended		3 Months Ended		9 Months Ended		38 Months Ended
	Sep. 08, 2014	Aug. 04, 2011	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014 Dividend	Sep. 30, 2013 Dividend	Sep. 30, 2014
Common Stock Capitalization [Line Items]
Number of Dividends Authorized					3	3
Common Shares Issued And Outstanding Upon Conversion of All Convertible Securities			34,070,643	26,031,717	34,070,643	26,031,717	34,070,643
Shareholders Equity Per Share Upon Conversion Of All Convertible Units (in usd per share)			$ 23.79	$ 24.19	$ 23.79	$ 24.19	$ 23.79
Dividends (in usd per share)			$ 0.77	$ 0.77	$ 2.31	$ 3.06
Payments of Dividends			$ (20,100,000)	$ (20,000,000)	$ (60,210,000)	$ (72,016,000)
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
Stock Issued During Period, Shares, New Issues	8,000,000		8,000,000	0	8,000,000	5,000,000
Net proceeds from share issuance	$ 188,200,000