Stockholders' Equity (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock option activity
Exercised (in shares)	(1,462,369)	(876,115)	(575,944)
Stock Options
Stock option activity
Outstanding at the beginning of the period (in shares)	4,749,449
Granted (in shares)	723,869
Exercised (in shares)	(1,414,369)
Forfeited (in shares)	(4,178)
Outstanding at the end of the period (in shares)	4,054,771	4,749,449
Exercisable at the end of the year (in shares)	4,054,771
Employee stock options, Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	56.06
Granted (in dollars per share)	129.49
Exercised (in dollars per share)	34.16
Forfeited (in dollars per share)	34.35
Outstanding at the end of the period (in dollars per share)	76.83	56.06
Exercisable at the end of year (in dollars per share)	76.83
Employee stock options, Weighted Average Remaining Contractual Term
Outstanding at the end of the year	6 years 4 months 24 days
Exercisable at the end of the year	6 years 4 months 24 days
Employee stock options, Aggregate Intrinsic Value
Outstanding at the end of the year (in dollars)	213,505,000
Exercisable at the end of the year (in dollars)	213,505,000
Weighted-average fair value of employee stock option granted (in dollars per share)	40.70	36.10	19.74
Total fair value of vested employee options	29,500,000	36,100,000	3,000,000