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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share Reconciliation [Line Items]
Net income (loss)	$ 27,716	$ 7,799	$ 10,943	$ (23,641)	$ (76,361)	$ 17,831	$ 18,074	$ 8,555	$ 19,327	$ 22,544	$ 12,688	$ 9,374	$ 22,817	$ (31,901)	$ 63,933
Denominator for basic earnings per share - weighted-average number of common shares outstanding during the period													46,332	49,680	49,298
Denominator for diluted earnings per share													46,655	49,680	49,825
Basic earnings per share	$ 0.64	$ 0.17	$ 0.23	$ (0.49)	$ (1.54)	$ 0.36	$ 0.36	$ 0.17	$ 0.39	$ 0.46	$ 0.26	$ 0.19	$ 0.49	$ (0.64)	$ 1.3
Diluted earnings per share	$ 0.64	$ 0.17	$ 0.23	$ (0.49)	$ (1.54)	$ 0.35	$ 0.36	$ 0.17	$ 0.39	$ 0.46	$ 0.26	$ 0.19	$ 0.49	$ (0.64)	$ 1.28
Stock Options [Member]
Earnings Per Share Reconciliation [Line Items]
Incremental common shares attributable to stock-based awards													104	0	313
Restricted Stock Units [Member]
Earnings Per Share Reconciliation [Line Items]
Incremental common shares attributable to stock-based awards													219	0	214