Equity Incentive Plans (Tables)

12 Months Ended

Dec. 31, 2019

Summary of Activity Under 2008 Plan, 2014 Plan and Inducement Plan Including Grants to Nonemployees Issued

		Options Issued and Outstanding			Weighted
			Weighted-Average		Average
	Shares Available		Exercise Price per		Remaining	Aggregate
	for Grant	Number of Shares	Share		ContractualTerm	Intrinsic Value
					(in Years)	(in thousands)
Balance at December 31, 2018	608,528	5,506,760	$	8.32
Options authorized	2,490,417	—	$	—
Options granted	(2,362,685)	2,362,685	$	2.56
Options exercised	—	(68,062)	$	2.59
Options canceled	528,615	(528,615)	$	7.69
Issuance of common stock for services	(113,136)	—		—
Forfeitures of PRSUs granted in prior years	45,007	—		—
Balance at December 31, 2019	1,196,746	7,272,768	$	6.55	7.40	$	19,128
Vested and expected to vest at December 31, 2019		6,754,711	$	6.74	7.30	$	17,217
Exercisable at December 31, 2019		4,183,281	$	7.95	6.46	$	8,753

Summary of Weighted-Average Assumptions to Estimate Fair Value of Stock Option Awards and Employee Stock Purchase Plan

	Year Ended December 31,
	2019
Expected term (years)	6.00
Expected volatility	81	%
Risk-free interest rate	2.42	%
Dividend yield	—	%

Summary of Non-Vested RSU Activity

					Weighted-
		Weighted-Average			Average Grant
	Number of	Grant Date Fair		Number of	Date Fair Value
	RSUs	Value Per Share		PRSUs	Per Share
Non-vested restricted stock units at December 31, 2018	85,609	$	4.70	894,764	$	4.30
Granted	—	$	—	—	$	—
Vested	(85,609)	$	4.70	—	$	—
Forfeited	—	$	—	(45,007)	$	4.30
Non-vested restricted stock units at December 31, 2019	—	$	—	849,757	$	4.30

Summary of Stock-Based Compensation Expense Recognized

	Year Ended December 31,
	2019		2018			2017
	(in thousands)
Research and development	$	4,104	$	3,666	$	4,585
General and administrative		5,832		5,560		5,005
Total	$	9,936	$	9,226	$	9,590

Summary of Stock-Based Compensation Expense Not Yet Recognized

	At December 31, 2019
	Unrecognized Compensation Expense		Average Vesting Period
	(in thousands)		(Years)
Stock options grants	$	8,277	2.5
PRSU grants	$	965	0.7
ESPP	$	53	0.2

2014 Employee Stock Purchase Plan [Member]

Summary of Activity Under 2008 Plan, 2014 Plan and Inducement Plan Including Grants to Nonemployees Issued

	Shares Available	Number of Shares	Purchase Price
	for Grant	Purchased	per Share		Gross Proceeds
					(in thousands)
Balance at December 31, 2018	680,322	330,936
Shares purchased	(160,744)	160,744	$	2.48	$	396
Balance at December 31, 2019	519,578	491,680

Summary of Weighted-Average Assumptions to Estimate Fair Value of Stock Option Awards and Employee Stock Purchase Plan

	Year Ended December 31,
	2019
Expected term (years)	0.5
Expected volatility	69	%
Risk-free interest rate	2.20	%
Dividend yield	—	%