Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock Option Activity

The following is a summary of option activity under the Stock Incentive Plans and Inducement Plan (in thousands, except share and per share amounts):

						Weighted-Average
				Weighted-Average		Remaining
	Number of			Exercise Price Per		Contractual Term		Aggregate Intrinsic
	Shares			Share		(In years)		Value
Outstanding at December 31, 2018		4,241,833		$	6.98		7.02	$	471
Granted		2,747,700			2.11
Exercised		(2,119	)		2.01				1
Forfeited		(426,960	)		5.06
Canceled		(207,124	)		8.62
Outstanding at December 31, 2019		6,353,330			4.95		7.29		229
Exercisable at December 31, 2019		3,242,751			6.84		5.55		33
Vested or expected to vest at December 31, 2019		5,751,313		$	5.16		7.09	$	199

Schedule of Estimated Assumptions Used to Calculate Weighted-Average Grant Date Fair Value of Options Granted

The total intrinsic value of options exercised in the year ended December 31, 2019 was immaterial. The total intrinsic value of options exercised in the years ended December 31, 2018 and 2017 were $1.4 million and $0.6 million, respectively. The weighted‑average fair values of options granted in the years ended December 31, 2019, 2018, and 2017 were $1.41, $3.54, and $2.95 per share, respectively, and were calculated using the following estimated assumptions:

	Year ended
	December 31,
	2019			2018			2017
Weighted-average risk-free interest rate		1.97	%		2.67	%		1.99	%
Expected dividend yield		0.00	%		0.00	%		0.00	%
Expected volatility		78	%		68	%		60	%
Expected terms	6.0 years			6.0 years			6.0 years

Schedule of Nonvested Restricted Stock Units Activity

The following is a summary of restricted stock unit activity under the 2014 Plan (in thousands, except share and per share amounts):

				Weighted-Average
	Number of			Grant Date Fair
	Shares			Value
Nonvested at December 31, 2018		1,198,634		$	5.04
Granted		589,142			3.23
Vested		(189,129	)		6.41
Forfeited		(303,139	)		4.33
Canceled		—			—
Nonvested at December 31, 2019		1,295,508		$	4.19

Schedule of Estimated Assumptions Used to Calculate Weighted-Average Fair Value of the Purchase Rights Granted

The fair value of the purchase rights granted under this plan was estimated on the date of grant and uses the following weighted-average assumptions, which were derived in a manner similar to those discussed in Note 2 relative to stock options:

	Year ended
	December 31,
	2019			2018			2017
Weighted-average risk-free interest rate		2.44	%		2.24	%		1.03	%
Expected dividend yield		0.00	%		0.00	%		0.00	%
Expected volatility		71	%		70	%		68	%
Expected terms	0.5 years			0.5 years			0.5 years

Summary of Stock-Based Compensation Expense for Stock Options Granted that was Recorded in the Company's Results of Operations

The following table summarizes the stock-based compensation expense resulting from awards granted under Stock Incentive Plans, the Inducement Plan and 2014 ESPP, that was recorded in the Company’s results of operations for the years presented (in thousands):

	Year ended
	December 31,
	2019		2018		2017
Cost of product revenue	$	365	$	803	$	125
Research and development		1,184		1,603		1,384
Selling, general and administrative		3,888		7,362		3,196
Total stock-based compensation expense	$	5,437	$	9,768	$	4,705