Stockholders' Equity (Details 5) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Numerator:
Income from continuing operations									$ 304,442	$ 217,243	$ 111,206
Income (loss) from discontinued operations										625	(5,290)
Net income	$ 83,255	$ 78,111	$ 72,316	$ 70,760	$ 43,189	$ 84,398	$ 73,891	$ 16,390	$ 304,442	$ 217,868	$ 105,916
Denominator:
Weighted average outstanding shares-basic									52,093	57,163	56,142
Effect of dilutive securities:
Convertible Senior Notes (in shares)									218	569	2,131
Warrants (in shares)										263
Stock options (in shares)									969	1,400	1,243
Weighted average shares-diluted									53,280	59,395	59,516
Basic
Continuing operations (in dollars per share)									$ 5.84	$ 3.80	$ 1.98
Discontinued operations (in dollars per share)									$ 0.00	$ 0.01	$ (0.09)
Net income per basic common share (in dollars per share)	$ 1.65	$ 1.52	$ 1.37	$ 1.32	$ 0.79	$ 1.45	$ 1.27	$ 0.28	$ 5.84	$ 3.81	$ 1.89
Diluted
Continuing operations (in dollars per share)									$ 5.71	$ 3.66	$ 1.87
Discontinued operations (in dollars per share)									$ 0.00	$ 0.01	$ (0.09)
Net income per diluted common share (in dollars per share)	$ 1.60	$ 1.46	$ 1.34	$ 1.29	$ 0.77	$ 1.38	$ 1.18	$ 0.26	$ 5.71	$ 3.67	$ 1.78
Stock options and warrants excluded from calculation (in shares)									11,862	16,299	13,532