Accounting for Shared-Based Payments (Details) (USD $)	3 Months Ended		9 Months Ended				3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Jan. 17, 2013 2008 Equity Compensation Incentive Plan	Dec. 31, 2012 2008 Equity Compensation Incentive Plan	Sep. 30, 2014 Research and development	Sep. 30, 2013 Research and development	Sep. 30, 2014 Research and development	Sep. 30, 2013 Research and development	Sep. 30, 2014 General and administrative	Sep. 30, 2013 General and administrative	Sep. 30, 2014 General and administrative	Sep. 30, 2013 General and administrative	Sep. 30, 2014 Stock options	Sep. 30, 2013 Stock options	Sep. 30, 2014 Stock options Minimum [Member]	Sep. 30, 2014 Stock options Maximum
Shared-based payments
Amount of excess tax benefits recognized (in dollars)			$ 0
Vesting period															3 years
Contractual term															10 years
Number of shares reserved under the plan					15,000,000	7,500,000
Total stock-based compensation expense (in dollars)	922,000	1,090,000	3,187,000	3,258,000			522,000	391,000	1,391,000	1,082,000	400,000	699,000	1,796,000	2,176,000
Unrecognized compensation cost related to non-vested employee stock options, net of expected forfeitures (in dollars)															$ 6,200,000
Weighted-average remaining vesting period over which unrecognized compensation cost is to be recognized															1 year 7 months 6 days
Number of stock options which vest upon a change of control (in shares)															4,364,000
Weighted-average assumptions used to estimate fair value of stock option awards using the Black-Scholes option valuation model
Risk-free interest rate, minimum (as a percent)															1.78%	0.41%
Risk-free interest rate, maximum (as a percent)															2.30%	2.64%
Expected volatility (as a percent)																60.00%	52.00%	60.00%
Expected term															6 years	6 years