Organization and Summary of Significant Accounting Policies (Tables)

6 Months Ended

Jun. 30, 2016

Accounting Policies [Abstract]

Schedule of Fair Value Measurements, Recurring and Nonrecurring Assets and Liabilities

The following table presents the Company’s fair value hierarchy for its warrant liabilities measured at fair value on a recurring basis (in thousands) as of June 30, 2016 and December 31, 2015:

	Quoted  Market  Prices for Identical Assets (Level 1)		Significant  Other Observable Inputs (Level 2)		Significant Unobservable Inputs  (Level 3)		Total
Warrant liabilities
Balance as of June 30, 2016	$	—	$	—	$	2,211	$	2,211
Balance as of December 31, 2015	$	—	$	—	$	1,841	$	1,841

Summary of Fair Value Measurements, Recurring and Nonrecurring, Valuation Assumptions

The following assumptions were used in determining the fair value of the common stock warrant liabilities valued using the Black-Scholes option pricing model as of June 30, 2016 and December 31, 2015:

	June 30, 2016			December 31, 2015
Risk-free interest rate	1.08		%	1.82		%
Volatility	85.71%-88.67%			83.00		%
Dividend yield	—		%	—		%
Expected term	6.54-6.68			6.13
Weighted average fair value	$	0.25		$	0.61

Summary of Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation

The following table is a reconciliation for all liabilities measured at fair value using Level 3 unobservable inputs (in thousands):

	Warrant liability
Balance as of December 31, 2015	$	1,841
Issuance of warrants in connection with January 2016 financing	4,807
Change in fair value measurement of warrant liability	(5,113		)
Repricing of February 2015 warrants in connection with January 2016 financing	676
Balance as of June 30, 2016	$	2,211

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share

The following securities that could potentially decrease net loss per share in the future are not included in the determination of diluted loss per share as their effect is anti-dilutive:

	As of June 30,
	2016	2015
Outstanding stock options	4,924,921	4,474,736
Outstanding warrants	14,519,169	6,859,682
Restricted stock	1,155,759	—

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions

The following table presents the assumptions used by the Company to estimate the fair value of stock option grants using the Black-Scholes option-pricing model, as well as the resulting weighted average fair values:

	Six Months Ended   June 30,
	2016			2015
Risk-free interest rate	1.36%-1.78%			1.39% - 1.69%
Volatility	72.35%-80.02%			81.13%-101.54%
Dividend yield	—		%	—		%
Expected term	5.25-6.08 years			5.25- 6.08 years
Forfeiture rate	11.33		%	11.54		%
Weighted average fair value	$	0.72		$	1.06

Summary of Stock Option Activity

A summary of the Company’s stock option activity under its stock option plans during the six months ended June 30, 2016 is as follows (in thousands):

	Number of Shares		Weighted Average Exercise Price
Outstanding as of December 31, 2015	4,054		$	1.95
Granted	1,667		$	1.06
Exercised	—		$	—
Cancelled	(796	)	$	1.71
Outstanding as of June 30, 2016	4,925		$	1.68

Summary of Restricted Stock Unit Activity

A summary of the Company’s restricted stock unit activity under its stock option plans during the six months ended June 30, 2016 is as follows (in thousands):

	Number of Shares		Weighted Average Grant Date Fair Value
Unvested as of December 31, 2015	—		$	—
Granted	1,278		$	0.43
Vested	(122	)	$	0.30
Forfeited	—		$	—
Unvested as of June 30, 2016	1,156		$	0.44

Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan

The following table summarizes the total stock-based compensation expense resulting from share-based awards recorded in the Company’s condensed consolidated statements of operations (in thousands):

	Three Months Ended   June 30,				Six Months Ended   June 30,
	2016		2015		2016		2015
Research and development	$	362	$	57	$	425	$	87
General and administrative	377		268		669		526
Total	$	739	$	325	$	1,094	$	613