Stock-based compensation (Tables)

9 Months Ended

Sep. 30, 2018

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Summary of Stock-Based Compensation Expense by Award Type

Stock-based compensation expense by award type included within the condensed consolidated statements of operations and comprehensive loss was as follows (in thousands):

	For the				For the
	three months ended September 30,				nine months ended September 30,
	2018		2017		2018		2017
Stock options	$	22,663	$	10,786	$	60,890	$	30,892
Restricted stock units		6,918		3,067		19,413		7,659
Employee stock purchase plan		216		130		546		402
	$	29,797	$	13,983	$	80,849	$	38,953

Schedule of Stock-Based Compensation Expense by Classification

Stock-based compensation expense by classification included within the condensed consolidated statements of operations and comprehensive loss was as follows (in thousands): 

	For the				For the
	three months ended September 30,				nine months ended September 30,
	2018		2017		2018		2017
Research and development	$	14,445	$	7,049	$	40,265	$	19,500
General and administrative		15,352		6,934		40,584		19,453
	$	29,797	$	13,983	$	80,849	$	38,953

Summary of Stock Option Activity Under Plan

The following table summarizes the stock option activity under the Company’s equity award plans:

	Shares (in thousands)			Weighted- average exercise price per share
Outstanding at December 31, 2017		3,755		$	67.91
Granted		1,416		$	193.00
Exercised		(535	)	$	52.87
Canceled or forfeited		(97	)	$	134.63
Outstanding at September 30, 2018		4,539		$	107.28
Exercisable at September 30, 2018		2,035		$	60.91
Vested and expected to vest at September 30, 2018		4,507		$	107.32

Restricted Stock Units [Member]

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Summary of Restricted Common Stock Awards

The following table summarizes the restricted stock unit activity under the Company’s equity award plans:

	Shares (in thousands)			Weighted- average grant date fair value
Unvested balance at December 31, 2017		477		$	80.72
Granted		626		$	197.79
Vested		(132	)	$	81.80
Forfeited		(37	)	$	159.04
Unvested balance at September 30, 2018		934		$	155.94