Stock-based compensation (Tables)

6 Months Ended

Jun. 30, 2020

Share-based Payment Arrangement [Abstract]

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 three months ended June 30,				For the six months ended June 30,
	2020		2019		2020		2019
Stock options	$	26,073	$	24,800	$	50,513	$	47,983
Restricted stock units	14,143		30,012		25,996		38,893
Employee stock purchase plan and other	8,313		299		8,313		576
	$	48,529	$	55,111	$	84,822	$	87,452

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 three months ended June 30,				For the six months ended June 30,
	2020		2019		2020		2019
Research and development	$	23,098	$	29,694	$	39,367	$	45,210
Selling, general and administrative	25,431		25,417		45,455		42,242
	$	48,529	$	55,111	$	84,822	$	87,452

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, 2019	5,483	$	116.30
Granted	1,306	$	72.50
Exercised	(27)	$	40.91
Canceled, forfeited, or expired	(296)	$	135.10
Outstanding at June 30, 2020	6,466	$	106.90
Exercisable at June 30, 2020	3,442	$	102.07
Vested and expected to vest at June 30, 2020	6,466	$	106.90

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, 2019	1,127	$	146.10
Granted	879	$	72.59
Vested	(318)	$	143.73
Forfeited	(95)	$	132.84
Unvested balance at June 30, 2020	1,593	$	106.81