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		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings per Share [Line Items]
Net income	$ 21,798	$ 33,154	$ 28,165	$ 69,774
Basic weighted-average shares outstanding (in shares)	40,846,315	40,744,667	40,831,296	40,732,704
Diluted weighted-average shares outstanding (in shares)	40,985,088	40,889,280	40,966,869	40,860,978
Basic net income per share (in dollars per share)	$ 0.53	$ 0.81	$ 0.69	$ 1.71
Diluted net income per share (in dollars per share)	$ 0.53	$ 0.81	$ 0.69	$ 1.71
Total anti-dilutive shares excluded from the calculation (in shares)	36	0	0	0
Performance shares [Member]
Earnings per Share [Line Items]
Incremental shares (in shares)	118,149	114,579	115,534	98,877
Restricted stock units [Member]
Earnings per Share [Line Items]
Incremental shares (in shares)	20,624	27,816	20,039	27,416
Stock options [Member]
Earnings per Share [Line Items]
Incremental shares (in shares)	0	2,218	0	1,981