Stock-Based Compensation

3 Months Ended

Mar. 31, 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 options granted to employees and consultants for all periods presented (in thousands):

	Three Months Ended March 31,
	2018		2017
Research and development	$	1,591	$	590
General and administrative		2,040		815
Total	$	3,631	$	1,405

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 and Awards			Exercise Price per Share
Balance at December 31, 2017		2,964,549		$	11.54
Options and awards granted		991,932			52.05
Options exercised		(110,961	)		7.26
Options and awards canceled		(52,156	)		19.13
Balance at March 31, 2018		3,793,364			22.15

In relation to stock options to purchase common stock that vest upon the achievement of performance criteria, $153,000 and $174,000 in stock-based compensation expense was recorded for the three months ended March 31, 2018 and 2017, respectively. The Company begins to recognize expenses related to these options during the period upon concluding that certain performance criteria are considered probable.