Stock-Based Compensation

6 Months Ended

Jun. 30, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

8. Stock-Based Compensation

The Company classifies stock-based compensation expense in the accompanying condensed consolidated statements of operations and comprehensive loss based on the department to which a recipient belongs. The following table sets forth stock-based compensation expense related to equity awards granted to employees and consultants for all periods presented (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
Research and development	$	2,050	$	610	$	3,641	$	1,200
General and administrative		2,732		731		4,772		1,546
Total	$	4,782	$	1,341	$	8,413	$	2,746

The following summarizes option and other equity award activity under the 2012 Equity Incentive Plan and 2015 Stock Option and Incentive Plan:

	Shares Subject to			Weighted Average
	Outstanding Options			Exercise Price per Share
Balance at December 31, 2017		2,964,549		$	11.54
Options granted		1,167,256			51.41
Options exercised		(263,145	)		7.31
Options canceled/forfeited		(99,248	)		20.26
Balance at June 30, 2018		3,769,412		$	23.95

	Shares Subject to			Weighted Average
	Outstanding Awards			Grant Date Fair Value
Balance at December 31, 2017		—		$	—
Restricted stock units granted		138,086			51.88
Restricted stock units forfeited		(2,830	)		53.77
Balance at June 30, 2018		135,256		$	51.84

Restricted stock units (“RSUs”) settle into shares of common stock upon vesting and the exercise price is the market price on the date of vesting.

Pursuant to the terms of the Company’s 2015 Employee Stock Purchase Plan (the “2015 ESPP”), on April 30, 2018, the Company issued 12,847 shares to participants in the 2015 ESPP in exchange for their contributions during the period from November 1, 2017 to April 30, 2018.

In relation to stock options and awards to purchase common stock that vest upon the achievement of performance criteria, $40,000 and zero in stock-based compensation expense was recorded for the three months ended June 30, 2018 and 2017, respectively, and $193,000 and $174,000 in stock-based compensation expense was recorded for the six months ended June 30, 2018 and 2017, respectively. The Company begins to recognize expenses related to these stock options and awards during the period upon concluding that certain performance criteria are considered probable.