Net Income Per Share (Details) (USD $) In Thousands, except Share data	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Numerator:
Income from continuing operations (in dollars)	$ 107,358	$ 116,110	$ 189,171	$ 158,805
Income (loss) from discontinued operations		$ 53		$ (1,091)
Denominator:
Average number of common shares outstanding (in shares)	62,313,000	53,363,000	58,390,000	53,366,000
Effect of dilutive securities:
Stock awards (in shares)	393,000	507,000	370,000	583,000
Weighted average shares, diluted (in shares)	62,706,000	53,870,000	58,760,000	53,949,000
Income from continuing operations, basic (in dollars per share)	$ 1.72	$ 2.18	$ 3.24	$ 2.98
Loss from discontinued operations, basic (in dollars per share)				$ (0.02)
Net income per share, basic (in dollars per share)	$ 1.72	$ 2.18	$ 3.24	$ 2.96
Income from continuing operations, diluted (in dollars per share)	$ 1.71	$ 2.16	$ 3.22	$ 2.94
Loss from discontinued operations, diluted (in dollars per share)				$ (0.02)
Net income per share, diluted (in dollars per share)	$ 1.71	$ 2.16	$ 3.22	$ 2.92
Anti-dilutive securities excluded from earnings per share calculation (in shares)	50,814	32,266	29,038	22,872