Common Share Capitalization (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jun. 13, 2018
Common Stock Capitalization [Line Items]
Dividends declared (in usd per share)	$ 0.41	$ 0.45	$ 0.82	$ 0.90
Payments of Dividends	$ (12,700)	$ (14,800)	$ (25,501)	$ (29,579)
Common Shares Issued And Outstanding Upon Conversion of All Convertible Securities	30,854,762	32,794,236	30,854,762	32,794,236
Stock Repurchase Program, Number of Shares Authorized to be Repurchased					1,550,000
Shares repurchased	242,161	51,518	1,186,058	182,006
Stock Repurchased and Retired During Period, Value	$ 3,600		$ 17,593	$ 2,868
Stock Repurchases, Average Price Per Share	$ 14.98		$ 14.83