Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock Option Activity

The following table summarizes our stock option activity under our stock plans and related information:

	Options Outstanding			Weighted- Average Exercise Price
Balance at December 31, 2019		3,887,780		$	18.38
Options granted		1,279,300		$	67.08
Options forfeited		(8,000	)	$	30.03
Options exercised		(72,833	)	$	6.89
Balance at March 31, 2020		5,086,247		$	30.78
Vested and expected to vest		5,086,247		$	30.78
Exercisable as of March 31, 2020		2,483,500		$	11.12

Summary of Stock-based Compensation Expense

The following table summarizes total stock-based compensation expense related to our 2018 Equity Incentive Plan, 2008 Equity Incentive Plan and 2018 Employee Stock Purchase Plan (in thousands):

	Three Months Ended March 31,
	2020		2019
Research and development	$	2,343	$	1,150
General and administrative		2,046		1,055
Total	$	4,389	$	2,205