Stockholders' Equity (Details 3) (USD $)	12 Months Ended
	Dec. 31, 2013 item	Dec. 31, 2012	Dec. 31, 2011
Stock option
Number of stock-based compensation plans	5
Proceeds from stock option exercises
Stock-based compensation expenses	$ 13,259,000	$ 9,165,000	$ 3,980,000
Stock Options
Stock option
Vesting period	4 years
Award expiration from grant date	10 years
Number of Shares
Outstanding at beginning of the year (in shares)	6,854,369	6,670,335	5,679,003
Granted (in shares)	463,475	2,326,500	2,061,377
Forfeited (in shares)	(135,626)	(282,909)	(69,343)
Exercised (in shares)	(1,015,817)	(1,859,557)	(1,000,702)
Outstanding at end of the period (in shares)	6,166,401	6,854,369	6,670,335
Exercisable (vested) at end of the period (in shares)	4,086,272	3,226,280	3,533,766
Available for future grants at the end of the period (in shares)	968,154
Weighted Average Exercise Price
Outstanding at beginning of the year (in dollars per share)	$ 7.92	$ 3.60	$ 2.14
Granted (in dollars per share)	$ 14.25	$ 15.83	$ 6.60
Forfeited (in dollars per share)	$ 13.15	$ 8.67	$ 4.52
Exercised (in dollars per share)	$ 4.75	$ 2.19	$ 1.40
Outstanding at end of the period (in dollars per share)	$ 8.81	$ 7.92	$ 3.60
Exercisable at end of the period (in dollars per share)	$ 6.82
Weighted Average Contractual Life (years)
Outstanding at end of the period		7 years 6 months	7 years 3 months 18 days
Exercisable at end of the period	6 years 3 months 18 days
Intrinsic Value
Outstanding	57,358,729	35,977,101	78,699,148
Vested	46,133,626	27,902,361	48,073,129
Exercised	14,932,262	29,851,276	9,930,497
Proceeds from stock option exercises
Proceeds from stock option exercises	4,800,000	4,100,000
Stock Options | Minimum
Weighted Average Exercise Price
Exercised (in dollars per share)	$ 0.25	$ 0.25
Stock Options | Maximum
Weighted Average Exercise Price
Exercised (in dollars per share)	$ 20.39	$ 9.83
Restricted Stock Units
Proceeds from stock option exercises
Aggregate fair value of grant	10,200,000
Stock-based compensation expenses	4,200,000	800,000
Total unrecognized compensation cost, net of estimated forfeitures, related to unvested units	$ 8,900,000
Number of Shares
Outstanding at beginning of the year (in shares)	221,314
Granted (in shares)	684,084	223,814
Vested (in shares)	(92,338)
Forfeited (in shares)	(4,267)	(2,500)
Outstanding at end of the period (in shares)	808,793	221,314
Weighted Average Fair Value
Outstanding at beginning of the year (in dollars per share)	$ 17.27
Granted (in dollars per share)	$ 14.89	$ 17.30
Vested (in dollars per share)	$ 17.05
Forfeited (in dollars per share)	$ 15.70	$ 20.35
Outstanding at end of the period (in dollars per share)	$ 15.29	$ 17.27
Restricted Stock Units | Minimum
Stock option
Vesting period	1 year
Restricted Stock Units | Maximum
Stock option
Vesting period	3 years