Net Loss Per Share

12 Months Ended

Dec. 31, 2018

Earnings Per Share [Abstract]

Net Loss Per Share

10. Net Loss Per Share

Basic and diluted net loss per share was calculated as follows for the years ended December 31, 2018, 2017 and 2016:

	Year ended December 31,
	2018			2017			2016
Basic net loss per share:
Numerator:
Net loss (in thousands)	$	(372,882	)	$	(270,120	)	$	(158,987	)
Denominator:
Weighted average common stock outstanding -    basic		46,121,194			38,113,678			33,492,795
Dilutive effect of shares of common stock    equivalents resulting from common stock    options and restricted stock units		—			—			—
Weighted average common stock outstanding -    diluted		46,121,194			38,113,678			33,492,795
Net loss per share—basic and diluted	$	(8.08	)	$	(7.09	)	$	(4.75	)

The following common stock equivalents outstanding as of December 31, 2018, 2017 and 2016 were excluded from the calculation of diluted net loss per share for the periods presented because including them would have been anti-dilutive:

	Year ended December 31,
	2018		2017		2016
Stock options		6,758,420		4,915,956		3,985,935
Restricted stock units		13,500		29,100		—
Employee stock purchase plan		16,398		11,683		6,784
		6,788,318		4,956,739		3,992,719

Stock options and restricted stock units that are outstanding and contain performance-based vesting criteria for which the performance conditions have not been met are excluded from the calculation of common stock equivalents outstanding.