Net Income Per Share (Calculation Of Net Income Per Share) (Details) (USD $) In Thousands, except Per Share data	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Earnings Per Share Basic And Diluted [Line Items]
Net income	$ 44,168	$ 20,624	$ 107,298	$ 41,279
Net income available to common stockholders-basic	43,553	20,099	105,734	39,430
Basic weighted average shares	139,449	142,230	141,118	143,182
Basic net income per share	$ 0.31	$ 0.14	$ 0.75	$ 0.28
Net income available to common stockholders-diluted	43,556	20,099	105,740	39,430
Dilutive effect of potential common shares	984	770	1,255	1,145
Diluted weighted average shares	140,433	143,000	142,373	144,327
Diluted net income per share	$ 0.31	$ 0.14	$ 0.74	$ 0.27
Basic [Member]
Earnings Per Share Basic And Diluted [Line Items]
Income allocated to participating securities	615	525	1,564	1,849
Diluted [Member]
Earnings Per Share Basic And Diluted [Line Items]
Income allocated to participating securities	$ 612	$ 525	$ 1,558	$ 1,849