Stockholders' Equity (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Numerator:
Income from continuing operations	$ 78,111	$ 80,615	$ 221,187	$ 174,054
Income from discontinued operations		3,783		625
Net income	$ 78,111	$ 84,398	$ 221,187	$ 174,679
Denominator:
Weighted average outstanding shares-basic	51,514	58,321	52,626	58,087
Effect of dilutive securities:
Convertible Notes (in shares)	662	1,489	136	2,444
Stock options (in shares)	1,414	1,400	1,087	1,531
Weighted average shares-diluted	53,590	61,210	53,849	62,062
Basic
Continuing operations (in dollars per share)	$ 1.52	$ 1.38	$ 4.20	$ 3.00
Discontinued operations (in dollars per share)	$ 0.00	$ 0.07	$ 0.00	$ 0.01
Net income per basic common share (in dollars per share)	$ 1.52	$ 1.45	$ 4.20	$ 3.01
Diluted
Continuing operations (in dollars per share)	$ 1.46	$ 1.32	$ 4.11	$ 2.80
Discontinued operations (in dollars per share)	$ 0.00	$ 0.06	$ 0.00	$ 0.01
Net income per diluted common share (in dollars per share)	$ 1.46	$ 1.38	$ 4.11	$ 2.81
Stock options and warrants excluded from calculation (in shares)	11,026	7,992	11,761	6,446