Stockholders’ Equity (Tables)

12 Months Ended

Dec. 31, 2016

Convertible preferred stock as of December 31, 2015, consisted of the following:

	December 31, 2015
	Shares Authorized		Original Issue Price per Share		Shares Issued and Outstanding		Net Carrying Value		Aggregate Liquidation Preference
	(in thousands, except share and per share amounts)
Series Seed		1,400,000	$	2.2300		627,867	$	1,378	$	1,400
Series A		11,199,876		5.9727		5,022,876		28,757		30,000
Series B		8,570,366		11.1942		3,843,604		42,835		43,026
Series C		9,684,789		15.0256		4,325,954		62,780		65,000
Total convertible preferred stock		30,855,031				13,820,301	$	135,750	$	139,426

Stock-based compensation expense by category was as follows for the years ended December 31, 2016, 2015 and 2014:

	For the Year Ended December 31,
	2016		2015		2014
	(in thousands)
Research and development	$	1,042	$	932	$	387
General and administrative		962		359		128
Total stock-based compensation expense	$	2,004	$	1,291	$	515
Employees	$	1,869	$	413	$	142
Non-employees		135		878		373
Total stock-based compensation expense	$	2,004	$	1,291	$	515

The following table summarizes option activity for the years ended December 31, 2016 and 2015:

	Shares Available for Grant			Number of Options Outstanding			Weighted- Average Exercise Price Per Option		Weighted- Average Remaining Contract Term (Years)		Aggregate Intrinsic Value
											(in thousands)
Balance, December 31, 2014		977,297			784,790		$	0.83		9.01	$	1,074
Shares reserved for issuance		1,345,430			—			—
Options granted		(1,687,484	)		1,687,484		$	4.64
Options exercised		—			(51,994	)	$	1.34
Options forfeited		104,787			(104,787	)	$	1.01
Options cancelled		11,631			(11,631	)	$	1.59
Balance, December 31, 2015		751,661			2,303,862		$	3.60		9.18	$	13,593
Increase to authorized shares		1,500,000			—
Options granted		(620,702	)		620,702		$	11.78
Options exercised		—			(129,809	)	$	1.21
Options forfeited		259,599			(259,599	)	$	4.83
Options cancelled		534			(534	)	$	5.44
Balance, December 31, 2016		1,891,092			2,534,622		$	5.60		8.50	$	32,126
Exercisable, December 31, 2016					905,669		$	2.79		7.66	$	14,021
Vested and expected to vest, December 31, 2016					2,386,820		$	5.42		8.39	$	30,685

The fair value of stock options for employees was estimated using a Black-Scholes option pricing model with the following assumptions:

The fair value of stock options for non-employees was estimated using a Black-Scholes option pricing model with the following assumptions: