Net Income Per Share (Calculation Of Net Income Per Share) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Earnings Per Share Basic And Diluted [Line Items]
Net income	$ 48,334	$ 26,705
Net income available to common stockholders - basic	48,069	26,292
Net income available to common stockholders-diluted	48,070	26,293
Basic weighted average shares	139,384	142,653
Basic net income per share	$ 0.34	$ 0.18
Dilutive effect of potential common shares	1,059	1,483
Diluted weighted average shares	140,443	144,136
Diluted net income per share	$ 0.34	$ 0.18
Basic [Member]
Earnings Per Share Basic And Diluted [Line Items]
Income allocated to participating securities	265	413
Diluted [Member]
Earnings Per Share Basic And Diluted [Line Items]
Income allocated to participating securities	$ 264	$ 412