Common Share Capitalization (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Aug. 03, 2015
Common Stock Capitalization [Line Items]
Dividends (in usd per share)	$ 1.95	$ 2.45	$ 3.08
Payments of Dividends	$ 65,148	$ 83,460	$ 86,449
Common Shares Issued And Outstanding Upon Conversion of All Convertible Securities	32,976,242	33,787,950	34,090,992
Stock Repurchase Program, Number of Shares Authorized to be Repurchased				1,700,000
Shares repurchased	833,784	325,613	0
Stock Repurchased and Retired During Period, Value	$ 14,028	$ 5,639	$ 0
Stock Repurchases, Average Price Per Share	$ 16.82