Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Share-based Payment Arrangement [Abstract]

Summary of stock option activity

The following table summarizes stock option activity during the twelve months ended December 31, 2019:

	Shares			Weighted average exercise price		Weighted average remaining contractual life (years)		Aggregate intrinsic value (in thousands)
Outstanding at January 1, 2019		1,132,618		$	48.52
Options granted		378,500			118.70
Options exercised		(20,131	)		11.67
Options cancelled		(29,000	)		175.78
Outstanding at December 31, 2019		1,461,987		$	64.67		7.37	$	68,604
Exercisable at December 31, 2019		943,399		$	40.38		6.94	$	63,995

Summary of unvested restricted share activity

The following table summarizes restricted share activity during the year ended December 31, 2019:

	Shares			Weighted average exercise price
Outstanding at January 1, 2019		52,063		$	9.45
Vested		(52,063	)		9.45
Outstanding at December 31, 2019		—		$	—

Schedule of stock-based compensation expense

Stock-based compensation expense during the years ended December 31, 2019, 2018 and 2017 was as follows (in thousands):

	Years Ended December 31,
	2019		2018		2017
Stock-based compensation expense by type of award:
Stock options	$	22,487	$	12,997	$	2,662
Restricted stock		272		492		592
Total stock-based compensation expense	$	22,759	$	13,489	$	3,254
Effect of stock-based compensation expense by line item:
Research and development	$	8,277	$	3,707	$	883
General and administrative		14,482		9,782		2,371
Total stock-based compensation expense included in net loss	$	22,759	$	13,489	$	3,254