Summary of Significant Accounting Policies (Schedule 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, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Net Income	$ 54,563	$ 47,514	$ 38,264	$ 27,807	$ 141,134	$ 22,517	$ 23,219	$ 16,019	$ 168,148	$ 202,889	$ 79,129
Weighted average common shares outstanding									71,694	72,270	72,057
Dilutive effect of stock-based awards									363	288	336
Shares used in computing diluted earnings per share									72,057	72,558	72,393
Basic earnings per share	$ 0.77	$ 0.67	$ 0.53	$ 0.38	$ 1.95	$ 0.31	$ 0.32	$ 0.22	$ 2.35	$ 2.81	$ 1.10
Diluted earnings per share	$ 0.77	$ 0.66	$ 0.53	$ 0.38	$ 1.94	$ 0.31	$ 0.32	$ 0.22	$ 2.33	$ 2.80	$ 1.09
Number of antidilutive options that were excluded from computation of earnings per share									0	0	0