Common Stock (Basic and Diluted Earnings Per Share) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Class of Stock Disclosures [Abstract]
Basic number of common shares outstanding									40,114,594	39,974,022	41,349,883
Dilutive effect of unvested performance awards									12,053	66,756	206,658
Dilutive effect of stock options									0	14,803	30,518
Diluted number of common shares outstanding									40,126,647	40,055,581	41,587,059
Net income	$ 1,191	$ 50,565	$ 29,193	$ 7,634	$ 4,819	$ 51,789	$ 30,894	$ 3,344	$ 88,583	$ 90,846	$ 103,539
Income allocated to participating restricted stock									(254)	(256)	(471)
Net income available to common shareholders basic									88,329	90,590	103,068
Income reallocated to participating restricted stock									(254)	(256)	(469)
Net income available to common shareholders diluted									$ 88,329	$ 90,590	$ 103,070
Earnings Per Share, Basic, Distributed									$ 1.045	$ 0.970	$ 0.660
Earnings Per Share, Basic, Undistributed									$ 1.155	$ 1.300	$ 1.830
Basic net income per common share	$ 0.03	$ 1.26	$ 0.73	$ 0.19	$ 0.12	$ 1.29	$ 0.77	$ 0.08	$ 2.200	$ 2.270	$ 2.490
Earnings Per Share, Diluted, Distributed									$ 1.045	$ 0.970	$ 0.660
Earnings Per Share, Diluted, Undistributed									$ 1.155	$ 1.290	$ 1.820
Diluted net income per common share	$ 0.03	$ 1.26	$ 0.72	$ 0.19	$ 0.12	$ 1.29	$ 0.77	$ 0.08	$ 2.200	$ 2.260	$ 2.480