Stock Incentive Plans (Tables)

3 Months Ended

Mar. 31, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Option, Unvested RSU Activity under 2014 Equity Incentive Plan and 2016 Inducement Plan and Related Information

The following table summarizes option and unvested RSU activity under the Company’s 2014 Equity Incentive Plan and 2016 Inducement Plan and related information:

	Shares Available for Grant			Stock Options Outstanding			Weighted- Average Exercise Price		Number of RSU Shares			Weighted- Average Grant Date Fair Value
Balance—December 31, 2017		156,429			1,941,473		$	4.21		439,926		$	4.39
Additional options authorized		357,075			—			—		—			—
Restricted stock grants		(8,846	)		—			—		—			—
RSUs granted		(78,934	)		—			—		78,934			6.31
RSUs forfeited		7,500			—			—		(7,500	)		5.20
RSUs vested		—			—			—		(69,556	)		4.24
Options granted		(159,534	)		159,534			3.61		—			—
Options exercised		—			(141,387	)		0.57		—			—
Options forfeited		17,792			(17,792	)		4.58		—			—
Options expired		1,817			(1,817	)		3.55		—			—
Balance—March 31, 2018		293,299			1,940,011		$	4.64		441,804		$	4.79

Summary of Options Outstanding and Exercisable Vested or Expected to Vest

Options outstanding that have vested and are expected to vest at March 31, 2018 are as follows:

	Number of Shares Issued		Weighted Average Exercise Price		Weighted Average Remaining Contractual Life (Years)		Aggregate Intrinsic Value (In Thousands)
Vested		927,362	$	4.89		6.85	$	3,022
Expected to vest		894,857		4.41		8.22		3,188
Total		1,822,219					$	6,210

Weighted-Average Assumptions Used to Estimate Fair Value of Share-Based Awards

The estimated fair values of employee stock options and ESPP shares were estimated using the Black-Scholes option-pricing model based on the following weighted-average assumptions:

	Three Months Ended March 31,
	2018			2017
Employee stock options
Expected term (in years)		6.0			6.0
Expected volatility		79.96	%	53.07%-53.36%
Risk-free interest rate		2.51	%	2.08%-2.12%
Expected dividend yield		—	%		—	%
Employee stock purchase plan
Expected term (in years)		0.5			0.5
Expected volatility		105.32	%		62.27	%
Risk-free interest rate		1.61	%		0.65	%
Expected dividend yield		—	%		—	%

Summary of Expense Relating to Employee and Nonemployee Stock-Based Payment Awards from Stock Options and RSUs

The following table summarizes stock-based compensation expense relating to employee and nonemployee stock options, RSUs and ESPP shares for the three months ended March 31, 2018 and 2017, included in the statements of operations as follows (in thousands):

	Three Months Ended March 31,
	2018		2017
Cost of testing	$	61	$	55
Research and development		213		64
Sales and marketing		64		38
General and administrative		368		234
Total	$	706	$	391