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, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounting Policies [Abstract]
Net Income	$ 36,648	$ 32,076	$ 31,848	$ 23,142	$ 32,709	$ 25,970	$ 25,632	$ 14,339	$ 123,714	$ 98,650	$ 86,785
Weighted average common shares outstanding									71,957	72,122	72,866
Dilutive effect of stock-based awards									599	616	562
Shares used in computing diluted earnings per share									72,556	72,738	73,428
Basic earnings per share	$ 0.51	$ 0.45	$ 0.44	$ 0.32	$ 0.45	$ 0.36	$ 0.36	$ 0.20	$ 1.72	$ 1.37	$ 1.19
Diluted earnings per share	$ 0.51	$ 0.44	$ 0.44	$ 0.32	$ 0.45	$ 0.36	$ 0.35	$ 0.20	$ 1.71	$ 1.36	$ 1.18
Number of antidilutive options that were excluded from computation of earnings per share									0	0	0