Common Stock (Basic And Diluted Earnings Per Share) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013	Mar. 31, 2012
Class of Stock Disclosures [Abstract]
Basic number of common shares outstanding	40,078,061	39,911,032	40,015,380	40,756,509
Dilutive effect of unvested performance awards	0	66,201	50,206	180,851
Dilutive effect of stock options	0	22,276	9,234	24,647
Diluted number of common shares outstanding	40,078,061	39,999,509	40,074,820	40,962,007
Net income	$ 7,634	$ 3,344	$ 95,136	$ 100,108
Income allocated to participating restricted stock	(26)	(24)	(248)	(440)
Net income available to common shareholders, basic	7,608	3,320	94,888	99,668
Income reallocated to participating restricted stock	(26)	(24)	(247)	(439)
Net income available to common shareholders, diluted	$ 7,608	$ 3,320	$ 94,889	$ 99,669
Earnings Per Share, Basic, Distributed	$ 0.25	$ 0.22	$ 1.00	$ 0.88
Earnings Per Share, Basic, Undistributed	$ (0.06)	$ (0.14)	$ 1.37	$ 1.57
Basic net income per common share	$ 0.19	$ 0.08	$ 2.37	$ 2.45
Earnings Per Share, Diluted, Distributed	$ 0.25	$ 0.22	$ 1.00	$ 0.88
Earnings Per Sare, Diluted, Undistributed	$ (0.06)	$ (0.14)	$ 1.37	$ 1.55
Diluted net income per common share	$ 0.19	$ 0.08	$ 2.37	$ 2.43