Net Loss per Share

12 Months Ended

Dec. 31, 2019

Earnings Per Share [Abstract]

Net Loss per Share

13. Net Loss per Share

Basic and diluted net loss per share attributable to common stockholders was calculated as follows:

	Year Ended December 31,
	2019			2018			2017
Numerator:
Net loss attributable to common stockholders	$	(70,279	)	$	(98,942	)	$	(89,380	)
Denominator:
Weighted average common shares outstanding, basic and    diluted		56,649,220			40,743,492			40,449,410
Net loss per share attributable to common stockholders, basic    and diluted	$	(1.24	)	$	(2.43	)	$	(2.21	)

The Company’s potential dilutive securities, which include stock options, unvested restricted common stock and shares issuable under the ESPP, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The following potential common shares, presented based on amounts outstanding at each period end, were excluded from the calculation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect:

	Year Ended December 31,
	2019		2018		2017
Stock options to purchase common stock		8,310,683		7,561,719		6,125,692
Unvested restricted stock units		130,000		226,900		356,778
Shares issuable under employee stock purchase plan		89,821		49,495		—
		8,530,504		7,838,114		6,482,470