Stock-based compensation (Tables)

9 Months Ended

Sep. 30, 2017

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,
	2017		2016		2017		2016
Stock options	$	10,786	$	8,294	$	30,892	$	26,278
Restricted stock units		3,067		1,495		7,659		4,248
Employee stock purchase plan		130		116		402		305
	$	13,983	$	9,905	$	38,953	$	30,831

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,
	2017		2016		2017		2016
Research and development	$	7,049	$	5,399	$	19,500	$	15,410
General and administrative		6,934		4,506		19,453		15,421
	$	13,983	$	9,905	$	38,953	$	30,831

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):

	Shares			Weighted-average exercise price per share
Outstanding at December 31, 2016		3,735		$	52.17
Granted		1,066		$	83.88
Exercised		(613	)	$	23.59
Canceled or forfeited		(172	)	$	83.09
Outstanding at September 30, 2017		4,016		$	63.62
Exercisable at September 30, 2017		2,037		$	49.05
Vested and expected to vest at September 30, 2017		4,016		$	63.62

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):

	Shares			Weighted-average grant date fair value
Unvested balance at December 31, 2016		263		$	63.07
Granted		297		$	84.79
Vested		(78	)	$	73.58
Forfeited		(26	)	$	63.18
Unvested balance at September 30, 2017		456		$	75.41