Stock-based Compensation (Tables)

6 Months Ended

Jun. 30, 2019

Share-based Payment Arrangement [Abstract]

Schedule of Allocated Stock-Based Compensation Expense

The Company recorded stock-based compensation expense related to stock options and shares issued under the Company's 2017 Employee Stock Purchase Plan (2017 Plan) in the following expense categories of its accompanying consolidated statements of operations for the three and six months ended June 30, 2019 and 2018:

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Cost of product sales	$	26	$	2	$	45	$	3
Research and development	284		166		527		405
General and administrative	2,387		1,932		4,545		3,715
	$	2,697	$	2,100	$	5,117	$	4,123

Schedule of Stock Option Activity

The following table summarizes the activity related to stock option grants to employees and nonemployees for the six months ended June 30, 2019:

	Shares		Weighted average exercise price per share		Weighted average remaining contractual life
Outstanding at December 31, 2018	6,182,873		$	10.60	6.67
Granted	2,013,173		7.73
Exercised	(93,587	)	3.98
Expired	—		—
Forfeited	(119,089	)	11.34
Outstanding at June 30, 2019	7,983,370		$	9.94	6.89
Exercisable at June 30, 2019	4,208,609		$	9.07	5.01
Vested and expected to vest at June 30, 2019	7,983,370		$	9.94	6.89

Schedule of Fair Value Options using Black-Scholes Pricing Model

The grant date fair value of each stock option grant was estimated at the time of grant using the Black-Scholes option-pricing model using the following weighted average assumptions:

	Six Months Ended June 30,
	2019			2018
Risk free interest rate	2.51		%	2.69		%
Expected term (in years)	6.05			5.90
Expected volatility	67.02		%	74.92		%
Annual dividend yield	0.00		%	0.00		%
Fair value of common stock	$	7.73		$	19.98

Schedule of Nonvested Restricted Stock Units Activity

The following table summarizes the activity related to restricted stock units (RSUs) granted to employees for the six months ended June 30, 2019:

	Shares
Balance at December 31, 2018	—
Granted	20,600
Vested and settled	—
Expired/ forfeited/ canceled	—
Balance at June 30, 2019	20,600
Expected to vest at June 30, 2019	20,600