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, 2015		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015		Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings per Share [Line Items]
Net income	$ 3,549		$ 21,798		$ 711		$ 5,656		$ 20,136		$ 33,154		$ 16,270		$ 20,350		$ 31,714	$ 89,910	$ 70,581
Basic weighted-average shares outstanding (in shares)																	40,842,126	40,748,924	40,502,878
Diluted weighted-average shares outstanding (in shares)																	40,987,819	40,894,382	40,709,287
Basic net income per share (in dollars per share)	$ 0.09	[1]	$ 0.53	[1]	$ 0.02	[1]	$ 0.14	[1]	$ 0.49	[1]	$ 0.81	[1]	$ 0.40	[1]	$ 0.50	[1]	$ 0.78	$ 2.21	$ 1.74
Diluted net income per share (in dollars per share)	$ 0.09	[1]	$ 0.53	[1]	$ 0.02	[1]	$ 0.14	[1]	$ 0.49	[1]	$ 0.81	[1]	$ 0.40	[1]	$ 0.50	[1]	$ 0.77	$ 2.20	$ 1.73
Anti-dilutive shares excluded from the calculation (in shares)																	0	1,216	3,441
Performance Shares [Member]
Earnings per Share [Line Items]
Incremental shares (in shares)																	122,334	117,830	133,766
Restricted Stock Units (RSUs) [Member]
Earnings per Share [Line Items]
Incremental shares (in shares)																	23,359	27,628	69,076
Stock Options [Member]
Earnings per Share [Line Items]
Incremental shares (in shares)																	0	0	3,567

[1] 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.