Common Share Capitalization (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands			12 Months Ended
	Sep. 08, 2014	May. 14, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Aug. 03, 2015
Common Stock Capitalization [Line Items]
Dividends (in usd per share)			$ 2.45	$ 3.08	$ 3.83
Payments of Dividends			$ 83,460	$ 86,449	$ 92,067
Common Shares Issued And Outstanding Upon Conversion of All Convertible Securities			33,787,950	34,090,992	26,051,238
Stock Repurchase Program, Number of Shares Authorized to be Repurchased						1,700,000
Shares repurchased			325,613	0	0
Stock Repurchased and Retired During Period, Value			$ 5,639	$ 0	$ 0
Stock Repurchases, Average Price Per Share			$ 17.32
Shares Issued	8,000,000	5,000,000	0	8,000,000	5,000,000
Net proceeds from share issuance	$ 188,200	$ 125,300