Common Share Capitalization (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Mar. 06, 2017
Common Stock Capitalization [Line Items]
Dividends declared (in usd per share)	$ 0.45	$ 0.50	$ 1.35	$ 1.50
Payments of Dividends	$ 14,800	$ 16,600	$ 44,336	$ 50,256
Common Shares Issued And Outstanding Upon Conversion of All Convertible Securities	32,680,917	33,286,926	32,680,917	33,286,926
Stock Repurchase Program, Number of Shares Authorized to be Repurchased					1,700,000
Shares repurchased	123,321	126,771	305,327	509,427
Stock Repurchased and Retired During Period, Value	$ 1,900		$ 4,791	$ 8,797
Stock Repurchases, Average Price Per Share	$ 15.60		$ 15.69