Common Share Capitalization (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Mar. 06, 2017
Common Stock Capitalization [Line Items]
Dividends (in usd per share)	$ 0.45	$ 0.50	$ 0.90	$ 1.00
Payments of Dividends	$ 14,800	$ 16,700	$ 29,579	$ 33,616
Common Shares Issued And Outstanding Upon Conversion of All Convertible Securities	32,794,236	33,405,294	32,794,236	33,405,294
Stock Repurchase Program, Number of Shares Authorized to be Repurchased					1,700,000
Shares repurchased	51,518	219,623	182,006	382,656
Stock Repurchased and Retired During Period, Value	$ 800		$ 2,868	$ 6,624
Stock Repurchases, Average Price Per Share	$ 15.81		$ 15.75