Earnings Per Share (Computation of Basic and Diluted Earnings Per Share ) (Details) (USD $) In Thousands, except Per Share data	3 Months Ended				6 Months Ended
	Jun. 30, 2011		Jun. 30, 2010		Jun. 30, 2011		Jun. 30, 2010
Earnings Per Share
Net income	$ 3,416		$ 21,109		$ 34,814		$ 44,849
Average shares used in basic computation	52,932		46,257		52,734		46,168
Dilutive effect of stock options and units	10,313	[1]	6,094	[1]	10,505	[1]	6,291	[1]
Weighted Average Number Diluted Shares Outstanding Adjustment, Total	63,245		52,351		63,239		52,459
Basic	$ 0.06		$ 0.46		$ 0.66		$ 0.97
Diluted	$ 0.05	[1]	$ 0.40	[1]	$ 0.55	[1]	$ 0.85	[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.