Convertible Preferred Stock (Details) $ / shares in Units, $ in Thousands			1 Months Ended	12 Months Ended
	Oct. 13, 2015 shares	Aug. 28, 2015 USD ($) $ / shares shares	Sep. 30, 2014 USD ($) Milestone director $ / shares shares	Dec. 31, 2015 USD ($) installment director $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)
Convertible Preferred Stock
Authorized (in shares)					34,090,000
Par value (in dollars per share) | $ / shares					$ 0.00001
New issues (in shares)				12,944,984	6,451,057
Issuance of convertible preferred stock | $				$ 39,864	$ 11,623
Temporary equity, issuance costs | $				$ 136	60
Fair value of preferred stock purchased put option on date of issuance | $					$ 1,039
Fair value assumptions
Preferred Shares Issued and Outstanding					27,341,057
Carrying Value | $					$ 36,677	$ 23,000	$ 21,260
Liquidation Preference | $					$ 35,882
Common Stock Issuable Upon Conversion					7,924,919
Dividends
Dividend rate, as a percent				8.00%
Conversion
Minimum net proceeds received in qualified public offering requiring mandatory conversion of temporary equity | $				$ 40,000
Minimum share price in qualified public offering requiring mandatory conversion of temporary equity (in dollars per share) | $ / shares				$ 12.80
Minimum percentage of holders required for determination of conversion date				60.00%
Conversion ratio					3.45
Common stock shares issued upon conversion of convertible preferred stock	11,677,076
Redemption
Minimum percentage of holders required for redemption				60.00%
Number of redemption installments | installment				3
Period before redemption				60 days
Number of Directors entitled to elect | director				3
Conversion of Stock, Shares Issued	11,677,076
Preferred Stock, Shares Authorized				10,000,000	0
Preferred Stock, Shares Outstanding				0
Series A convertible preferred stock
Convertible Preferred Stock
Authorized (in shares)					20,890,000
Issue price of shares (in dollars per share) | $ / shares				$ 1.00
Fair value assumptions
Preferred Shares Issued and Outstanding					20,890,000
Carrying Value | $					$ 24,879
Liquidation Preference | $					$ 25,023
Common Stock Issuable Upon Conversion					6,055,060
Conversion
Conversion price (in dollars per share) | $ / shares				3.45
Series B convertible preferred stock
Convertible Preferred Stock
Authorized (in shares)					13,200,000
New issues (in shares)			6,451,057
Issue price of shares (in dollars per share) | $ / shares			$ 1.65
Issuance of convertible preferred stock | $			$ 10,644
Temporary equity, issuance costs | $			$ 60
Fair value assumptions
Preferred Shares Issued and Outstanding					6,451,057
Carrying Value | $					$ 11,798
Liquidation Preference | $					$ 10,859
Common Stock Issuable Upon Conversion					1,869,859
Conversion
Conversion price (in dollars per share) | $ / shares				5.6925
Series B convertible preferred stock | Put option | Long position
Convertible Preferred Stock
Number of milestones to attain for call of purchased put option | Milestone			2
Number of shares that may be exercised under option			6,451,057
Price at which shares may be exercised under option (in dollars per share) | $ / shares			$ 1.65
Number of directors for confirming exercise of option | director			5
Percentage of voting stockholders for confirming exercise of option			60.00%
Fair value of preferred stock purchased put option on date of issuance | $			$ 1,039
Fair value assumptions
Risk-free interest rate assumption (as a percent)			0.08%
Expected term (in months)			9 months
Expected volatility (as a percent)			80.00%
Expected dividends | $ / shares			$ 0
Fair value of underlying instruments (as a percent) | $ / shares			$ 1.65
Probability of occurrence of successful attainment of specified milestones triggering exercise of option (as a percent)			60.00%
Probability of occurrence of option exercised when exercisable (as a percent)			60.00%
Series C convertible preferred stock
Convertible Preferred Stock
New issues (in shares)		12,944,984
Issue price of shares (in dollars per share) | $ / shares		$ 3.09
Issuance of convertible preferred stock | $		$ 40,000
Conversion
Conversion price (in dollars per share) | $ / shares				$ 10.6605