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, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Net income	$ 48,496	$ 39,044	$ 43,318	$ 36,086	$ 54,563	$ 47,514	$ 38,264	$ 27,807	$ 166,944	$ 168,148	$ 202,889
Weighted average common shares outstanding									69,567	71,694	72,270
Dilutive effect of stock-based awards									459	363	288
Shares used in computing diluted earnings per share									70,026	72,057	72,558
Basic earnings per share	$ 0.70	$ 0.56	$ 0.62	$ 0.51	$ 0.77	$ 0.67	$ 0.53	$ 0.38	$ 2.40	$ 2.35	$ 2.81
Diluted earnings per share	$ 0.70	$ 0.56	$ 0.62	$ 0.51	$ 0.77	$ 0.66	$ 0.53	$ 0.38	$ 2.38	$ 2.33	$ 2.80
Number of antidilutive options that were excluded from computation of earnings per share									0	0	0