Earnings per Share (Reconciliation Of Number Of Common Shares Used In Calculating Basic And Diluted EPS) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings per Share [Line Items]
Net income	$ 14,373		$ 27,646		$ (31,238)		$ 157		$ 3,549		$ 21,798		$ 711		$ 5,656		$ 10,938	$ 31,714	$ 89,910
Basic weighted-average shares outstanding																	40,797,806	40,842,126	40,748,924
Diluted weighted-average shares outstanding																	41,033,440	40,987,819	40,894,382
Basic net income per share	$ 0.35	[1]	$ 0.68	[1]	$ (0.77)	[1]	$ 0	[1]	$ 0.09	[1]	$ 0.53	[1]	$ 0.02	[1]	$ 0.14	[1]	$ 0.27	$ 0.78	$ 2.21
Diluted net income per share	$ 0.35	[1]	$ 0.68	[1]	$ (0.77)	[1]	$ 0	[1]	$ 0.09	[1]	$ 0.53	[1]	$ 0.02	[1]	$ 0.14	[1]	$ 0.27	$ 0.77	$ 2.20
Performance shares [Member]
Earnings per Share [Line Items]
Incremental shares																	200,164	122,334	117,830
Restricted stock units [Member]
Earnings per Share [Line Items]
Incremental shares																	35,470	23,359	27,628

[1] Per share amounts are computed independently for each of the quarters presented. Therefore, the sum of the quarterly per share amounts may not equal the total computed for the year.