Stock-Based Compensation (Details 2) (USD $)	3 Months Ended		0 Months Ended	1 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Feb. 28, 2015	Jun. 30, 2010 item
Stock-Based Compensation
Outstanding options fully vested and expected to vest (in shares)	9,027,000
Remaining contractual life of options fully vested and expected to vest	4 years 4 months 24 days
Weighted average exercise price of options fully vested and expected to vest (in dollars per share)	$ 3.58
Awards exercisable (in shares)	6,017,000
Weighted average exercise price of awards exercisable (in dollars per share)	$ 3.81
Options
Assumptions used in estimation of fair value of the share-based payment awards on the grant date
Risk-free interest rate, minimum (as a percent)	0.60%	1.50%
Risk-free interest rate, maximum (as a percent)	1.40%	1.70%
Volatility, minimum (as a percent)	55.80%	56.90%
Volatility, maximum (as a percent)	57.70%	57.50%
Dividend yield (as a percent)	0.00%	0.00%
Options | Minimum
Assumptions used in estimation of fair value of the share-based payment awards on the grant date
Expected life	3 years	4 years
Options | Maximum
Assumptions used in estimation of fair value of the share-based payment awards on the grant date
Expected life	5 years	5 years
ESPP
Employee Stock Purchase Plan
Number of shares reserved for issuance				2,000,000
Maximum amount of shares that eligible employee may purchase annually (in dollars)				$ 25,000
Number of offering periods				2
Offering period				6 months
Purchase price to be paid by participants as a percentage of price per share either at the beginning or the end of each six-month offering period, whichever is less				85.00%
Shares of common stock issued under the plan			154,000
Aggregate purchase price (in dollars)			$ 422,000
Shares authorized and unissued	427,000