Stock Based Awards (Tables)

12 Months Ended

Dec. 31, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock Option Activity

Activity under the Company’s stock option plans is set forth below:

									Weighted
									Average
							Weighted		Remaining		Aggregate
	Shares						Average		Contractual		Intrinsic
	Available			Number of			Exercise		Life		Value
	for Grant			Shares			Price		(in years)		(in thousands)
Balances, January 1, 2017		174,019			742,052		$	66.96
Additional shares authorized		261,329			—			—
Options granted		(227,450	)		227,450			95.50
Restricted stock units granted		(428,056	)		—			—
Options exercised		—			(141,833	)		17.62
Options cancelled		220,158			(220,158	)		87.90
Balances, December 31, 2017		—			607,511			81.60
Additional shares authorized		269,535			—			—
Assumption of option plans associated with the merger		660,151			1,183,950			0.44
Options granted		—			—			—
Restricted stock units granted		—			—			—
Options exercised		—			(3,643	)		9.66
Options cancelled		271,895			(271,895	)		80.09
Balances, December 31, 2018		1,201,581			1,515,923		$	18.65		6.5	$	3,650
Vested and expected to vest as of December 31, 2018					1,514,245		$	18.58		6.5	$	3,650
Exercisable as of December 31, 2018					1,469,854		$	16.76		6.5	$	3,650

Stock Options Outstanding and Exercisable under Stock Option Plans

The following table summarizes information with respect to stock options outstanding and currently exercisable and vested as of December 31, 2018:

					Options Exercisable
	Options Outstanding				and Vested
			Weighted Average				Weighted Average
			Remaining				Remaining
Range of	Number		Contractual		Number		Contractual
Exercise Prices	Outstanding		Life (in Years)		Outstanding		Life (in Years)
$0.06-$0.06		86,867		2.5		86,867		2.5
$0.24-$0.24		621,098		6.4		621,098		6.4
$0.66-$0.90		475,985		8.5		475,985		8.5
$7.59-$126.00		312,679		5.1		266,644		5.1
$127.80-$191.76		19,294		3.8		19,260		3.8
		1,515,923				1,469,854

Summary of Fair Value of Employee Stock Options

The fair value of employee stock options was estimated using the Black-Scholes model with the following weighted-average assumptions:

	Year Ended December 31,
	2018			2017
Expected volatility		132.0	%		78.0	%
Risk-free interest rate		3.0	%		2.1	%
Dividend yield		0.0	%		0.0	%
Expected life (in years)		3.3			6.2

Schedule of Estimated Stock-Based Compensation Expense

Stock-based compensation expense, net of estimated forfeitures, is reflected in the statements of operations and comprehensive loss as follows (in thousands):

	Year Ended December 31,
	2018		2017
Operating Expenses
Research and development	$	2,946	$	4,549
General and administrative		13,193		8,800
Total	$	16,139	$	13,349

Summary of Restricted Stock Activity

A summary of the Company’s restricted stock activity is presented in the following tables:

				Weighted
				Average
	Number of			Grant Date
	Shares			Fair Value
Restricted Stock Units
Unvested at December 31, 2017		419,163		$	32.56
Granted		—			—
Vested		(128,136	)		35.60
Forfeited/canceled		(173,430	)		31.12
Unvested at December 31, 2018		117,597		$	31.37