Stock-based compensation (Tables)

6 Months Ended

Jun. 30, 2016

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 June 30,				Six months ended June 30,
	2016		2015		2016		2015
Stock options	$	9,057	$	15,310	$	17,984	$	20,065
Restricted stock units		1,626		668		2,753		1,285
Employee stock purchase plan		99		72		189		132
	$	10,782	$	16,050	$	20,926	$	21,482

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 June 30,				Six months ended June 30,
	2016		2015		2016		2015
Research and development	$	5,330	$	12,066	$	10,011	$	15,300
General and administrative		5,452		3,984		10,915		6,182
	$	10,782	$	16,050	$	20,926	$	21,482

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, 2015		3,532		$	48.74
Granted		840		$	50.14
Exercised		(90	)	$	10.99
Canceled or forfeited		(179	)	$	46.13
Outstanding at June 30, 2016		4,103		$	49.97
Exercisable at June 30, 2016		1,788		$	32.76
Vested and expected to vest at June 30, 2016		4,049		$	49.45

Restricted Stock Units [Member]

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

Summary of Restricted Common Stock Awards

Restricted stock units

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, 2015		148		$	65.79
Granted		210		$	50.14
Vested		(8	)	$	179.30
Forfeited		(12	)	$	36.28
Unvested balance at June 30, 2016		338		$	54.26