Earnings Per Share (Computation 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, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Earnings Per Share [Abstract]
Net income	$ 39,954	$ 37,710	$ 26,136	$ 34,773	$ 27,016	$ 22,304	$ 3,416	$ 31,398	$ 138,573		$ 84,134		$ 1,907
Average shares used in basic computation									53,563		52,418		48,723
Dilutive effect of stock options and units									9,374		10,640		8,949
Average shares used in diluted computation									62,937		63,058		57,672
Basic	$ 0.74	$ 0.70	$ 0.49	$ 0.65	$ 0.52	$ 0.43	$ 0.06	$ 0.60	$ 2.59		$ 1.61		$ 0.04
Diluted	$ 0.63	$ 0.60	$ 0.42	$ 0.55	$ 0.43	$ 0.35	$ 0.05	$ 0.50	$ 2.20	[1]	$ 1.33	[1]	$ 0.03	[1]

[1] Diluted earnings per share is computed on the basis of the weighted average number of shares of common stock plus the effect of dilutive potential common shares outstanding during the period using the treasury stock method. Diluted earnings per share include stock options and units.