Stock-based compensation (Tables)

3 Months Ended

Mar. 31, 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):

	Three Months Ended March 31,
	2017		2016
Stock options	$	9,342	$	8,926
Restricted stock units		1,956		1,127
Employee stock purchase plan		183		90
	$	11,481	$	10,143

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): 

	Three Months Ended March 31,
	2017		2016
Research and development	$	5,654	$	4,681
General and administrative		5,827		5,462
	$	11,481	$	10,143

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		696		$	76.37
Exercised		(181	)	$	15.18
Canceled or forfeited		(47	)	$	88.88
Outstanding at March 31, 2017		4,203		$	57.35
Exercisable at March 31, 2017		2,070		$	42.63
Vested and expected to vest at March 31, 2017		4,203		$	57.35

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		205		$	78.88
Vested		(39	)	$	50.08
Forfeited		(3	)	$	57.10
Unvested balance at March 31, 2017		426		$	71.92