Stock-Based Compensation (Details 4) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Number of Shares
Outstanding at the beginning of the period (in shares)	18,066
Granted (in shares)	2,719
Exercised (in shares)	(90)
Forfeited (in shares)	(31)
Outstanding at the end of the period (in shares)	20,664	18,066
Number of stock option exercisable	14,177
Number of shares vested and expected to vest	20,154
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 3.50
Granted (in dollars per share)	$ 6.35
Exercised (in dollars per share)	$ 2.18
Forfeited (in dollars per share)	$ 6.76
Outstanding at the end of the period (in dollars per share)	$ 3.87	$ 3.50
Weighted average exercise price for exercisable option	$ 2.66
Weighted average exercise price of shares vested and expected to vest	$ 3.80
Weighted Average Remaining Contractual Term
Outstanding at the beginning of the period	6 years 8 months 16 days	6 years 6 months 14 days
Outstanding at the end of the period	6 years 8 months 16 days	6 years 6 months 14 days
Exercisable	5 years 6 months 7 days
Vested and expected to vest	6 years 7 months 20 days
Aggregate Intrinsic Value
Outstanding at the beginning of the period (in dollars)	$ 51,486
Outstanding at the end of the period (in dollars)	51,276	51,486
Options exercisable (in dollars)	49,725
Shares vested and expected to vest (in dollars)	$ 51,249