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, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Net Income	$ 21,811	$ 18,920	$ 18,306	$ 20,092	$ 36,648	$ 32,076	$ 31,848	$ 23,142	$ 79,129	$ 123,714	$ 98,650
Weighted average common shares outstanding									72,057	71,957	72,122
Dilutive effect of stock-based awards									336	599	616
Shares used in computing diluted earnings per share									72,393	72,556	72,738
Basic earnings per share	$ 0.30	$ 0.26	$ 0.25	$ 0.28	$ 0.51	$ 0.45	$ 0.44	$ 0.32	$ 1.10	$ 1.72	$ 1.37
Diluted earnings per share	$ 0.30	$ 0.26	$ 0.25	$ 0.28	$ 0.51	$ 0.44	$ 0.44	$ 0.32	$ 1.09	$ 1.71	$ 1.36
Number of antidilutive options that were excluded from computation of earnings per share									0	0	0