Stockholders' Equity (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Employee stock options activity
Exercise of stock options (in shares)	(575,944)	(837,690)	(3,335,114)
Stock Options
Employee stock options activity
Outstanding at the beginning of the period (in shares)	4,923,377
Granted (in shares)	153,225
Exercise of stock options (in shares)	(519,552)
Forfeited (in shares)	(6,000)
Outstanding at the end of the period (in shares)	4,551,050
Exercisable at the end of the period (in shares)	4,551,050
Employee stock options, Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	36.98
Granted (in dollars per share)	53.42
Exercised (in dollars per share)	24.89
Forfeited (in dollars per share)	7.58
Outstanding at the end of the period (in dollars per share)	38.95
Exercisable at the end of the period, Weighted-Average Exercise Price (in dollars per share)	38.95
Employee stock options, Weighted Average Remaining Contractual Term
Outstanding at the end the period	5 years 2 months 12 days
Awards exercisable at the end of the period	5 years 2 months 12 days
Employee stock options, Aggregate Intrinsic Value
Outstanding at the end of the period (in dollars)	71,162,000
Exercisable at the end of the period, Aggregate Intrinsic Value	71,162,000
Weighted-average fair value of employee stock option granted (in dollars per share)	19.74		26.14
Total fair value of vested employee options	3,000,000	1,600,000	29,000,000