Stockholders' Equity (Details 3) (USD $)	3 Months Ended						3 Months Ended
	Mar. 31, 2013 item	Mar. 31, 2012	Mar. 31, 2013 Stock Options	Mar. 31, 2013 Stock Options Minimum	Mar. 31, 2013 Stock Options Maximum	May 03, 2013 Stock Options Employee plan, the Executive plan, the 2005 plan or the 1999 plan	Mar. 31, 2013 Restricted Stock Units	Mar. 31, 2013 Restricted Stock Units Minimum	Mar. 31, 2013 Restricted Stock Units Maximum
Stock option
Number of stock-based compensation plans	5
Vesting period			4 years					2 years	4 years
Award expiration from grant date			10 years
Number of Shares
Outstanding at beginning of the year (in shares)			6,854,369
Granted (in shares)			391,275
Forfeited (in shares)			(31,671)
Exercised (in shares)			(100,671)
Outstanding at end of the period (in shares)			7,113,302
Exercisable at end of the period (in shares)			3,849,690
Available for future grants at the end of the period (in shares)			173,682			0
Weighted Average Exercise Price
Outstanding at beginning of the year (in dollars per share)			$ 7.92
Granted (in dollars per share)			$ 14.29
Forfeited (in dollars per share)			$ 10.48
Exercised (in dollars per share)			$ 2.97	$ 0.25	$ 12.56
Outstanding at end of the period (in dollars per share)			$ 8.33
Exercisable at end of the period (in dollars per share)			$ 5.06
Weighted Average Contractual Life (years)
Outstanding at end of the period			7 years 6 months
Exercisable at end of the period			6 years 4 months 24 days
Intrinsic Value
Outstanding			$ 37,296,821
Vested			29,926,026
Exercised			1,133,058
Proceeds from stock option exercises
Proceeds from stock option exercises			300,000
Aggregate fair value of grant							7,700,000
Stock-based compensation expenses	3,099,000	1,624,000					700,000
Total unrecognized compensation cost, net of estimated forfeitures, related to unvested units							$ 10,100,000
Number of Shares
Outstanding at beginning of the year (in shares)							221,314
Granted (in shares)							519,034
Vested (in shares)							(37,957)
Outstanding at end of the period (in shares)							702,391
Weighted Average Fair Value
Outstanding at beginning of the year (in dollars per share)							$ 17.27
Granted (in dollars per share)							$ 14.93
Vested (in dollars per share)							$ 16.29
Outstanding at end of the period (in dollars per share)							$ 15.59