Earnings 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
Anti-dilutive shares (in shares)			1,200,000	2,300,000
Net Income (Numerator)
Basic earnings - net income	$ 98,710	$ 49,207	$ 204,613	$ 114,176
5.125% convertible senior notes (in dollars)	2,358	2,377	4,716	4,754
Diluted earnings - net income (in dollars)	$ 101,068	$ 51,584	$ 209,329	$ 118,930
Shares (Denominator)
Weighted average common shares outstanding - basic (in shares)	218,500,000	216,635,000	218,246,000	216,459,000
Dilutive stock option effect (in shares)	1,384,000	1,583,000	1,617,000	1,789,000
5.125% convertible senior notes (in shares)	16,382,000	16,382,000	16,382,000	16,382,000
Weighted average common shares outstanding - diluted (in shares)	236,266,000	234,600,000	236,245,000	234,630,000
Per Share Amount
Basic earnings per share (in dollars per share)	$ 0.45	$ 0.23	$ 0.94	$ 0.53
Diluted earnings per share (in dollars per share)	$ 0.43	$ 0.22	$ 0.89	$ 0.51