Common Share Capitalization (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Aug. 03, 2015
Common Stock Capitalization [Line Items]
Dividends (in usd per share)	$ 0.65	$ 0.77	$ 1.95	$ 2.31
Payments of Dividends	$ 22,100	$ 20,100	$ 66,462	$ 60,210
Common Shares Issued And Outstanding Upon Conversion of All Convertible Securities	34,063,910	34,070,643	34,063,910	34,070,643
Stock Repurchase Program, Number of Shares Authorized to be Repurchased					1,700,000
Shares repurchased	34,507	0	34,507	0
Stock Repurchased and Retired During Period, Value	$ 623		$ 623	$ 0
Stock Repurchases, Average Price Per Share	$ 18.03