Summary of Significant Accounting Policies (Schedule Of Basic and Diluted Earnings Per Share) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounting Policies [Abstract]
Net Income	$ 32,709	$ 25,970	$ 25,632	$ 14,339	$ 22,175	$ 21,259	$ 25,840	$ 17,511	$ 98,650	$ 86,785	$ 103,034
Weighted average common shares outstanding									72,122	72,866	72,909
Dilutive effect of stock-based awards									616	562	544
Shares used in computing diluted earnings per share									72,738	73,428	73,453
Basic earnings per share	$ 0.45	$ 0.36	$ 0.36	$ 0.20	$ 0.31	$ 0.29	$ 0.35	$ 0.24	$ 1.37	$ 1.19	$ 1.41
Diluted earnings per share	$ 0.45	$ 0.36	$ 0.35	$ 0.20	$ 0.30	$ 0.29	$ 0.35	$ 0.24	$ 1.36	$ 1.18	$ 1.40
Number of antidilutive options that were excluded from computation of earnings per share									0	0	0