Accounting for Shared-Based Payments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Jun. 08, 2015	Dec. 31, 2014
Shared-based payments
Total stock-based compensation expense (income) (in dollars)	$ (69)	$ 922	$ 7,724	$ 3,187
Research and development | Employee
Shared-based payments
Total stock-based compensation expense (income) (in dollars)	592	522	1,702	1,391
General and administrative | Employee
Shared-based payments
Total stock-based compensation expense (income) (in dollars)	(661)	$ 400	$ 6,022	$ 1,796
2008 Equity Compensation Incentive Plan
Shared-based payments
Number of shares reserved under the plan					30,000,000	15,000,000
Stock options
Shared-based payments
Vesting period			3 years
Contractual term			10 years
Unrecognized compensation cost related to non-vested employee stock options, net of expected forfeitures (in dollars)	$ 16,500		$ 16,500
Weighted-average remaining vesting period over which unrecognized compensation cost is to be recognized			2 years 3 months
Number of stock options which vest upon a change of control (in shares)	4,364,000		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)			1.46%	1.78%
Risk-free interest rate, maximum (as a percent)			2.02%	1.98%
Expected volatility, minimum (as a percent)			57.00%
Expected volatility, maximum (as a percent)			80.00%
Expected volatility (as a percent)				60.00%
Expected term			6 years	6 years