Summary Of Significant Accounting Policies (Schedule Of Calculation Of Basic And Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share Reconciliation [Line Items]
Net income	$ 39,421	$ 20,565	$ 21,210	$ 14,205	$ 23,338	$ 16,906	$ 21,558	$ 19,439	$ 67,710	$ 23,648	$ 8,256	$ 11,331	$ 95,401	$ 81,241	$ 110,945
Denominator for basic earnings per share - weighted-average number of common shares outstanding during the period													51,573	53,538	54,213
Incremental common shares attributable to exercise of dilutive options													318	450	324
Incremental common shares attributable to outstanding restricted shares and restricted stock units													197	234	242
Denominator for diluted earnings per share													52,088	54,222	54,779
Basic earnings per share	$ 0.78	$ 0.4	$ 0.41	$ 0.27	$ 0.44	$ 0.32	$ 0.4	$ 0.36	$ 1.26	$ 0.44	$ 0.15	$ 0.21	$ 1.85	$ 1.52	$ 2.05
Diluted earnings per share	$ 0.77	$ 0.4	$ 0.4	$ 0.27	$ 0.44	$ 0.31	$ 0.4	$ 0.36	$ 1.25	$ 0.43	$ 0.15	$ 0.21	$ 1.83	$ 1.5	$ 2.03