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, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Net income	$ 60,556	$ 46,332	$ 39,132	$ 23,058	$ 48,496	$ 39,044	$ 43,318	$ 36,086	$ 169,078	$ 166,944	$ 168,148
Weighted average common shares outstanding									69,018	69,567	71,694
Dilutive effect of stock-based awards									409	459	363
Shares used in computing diluted earnings per share									69,427	70,026	72,057
Basic earnings per share	$ 0.88	$ 0.67	$ 0.57	$ 0.33	$ 0.70	$ 0.56	$ 0.62	$ 0.51	$ 2.45	$ 2.40	$ 2.35
Diluted earnings per share	$ 0.88	$ 0.67	$ 0.56	$ 0.33	$ 0.70	$ 0.56	$ 0.62	$ 0.51	$ 2.44	$ 2.38	$ 2.33
Number of antidilutive options that were excluded from computation of earnings per share									0	0	0