Income taxes (Tables)

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

Schedule Components of Loss Before Income Taxes

The components of loss before income taxes were as follows (in thousands):

	Year ended December 31,
	2020		2019		2018
U.S.	$	(489,091)	$	(649,172)	$	(440,473)
Foreign	(128,918)		(140,981)		(114,965)
Total	$	(618,009)	$	(790,153)	$	(555,438)

Summary of Provision for (Benefit from) Income Taxes

The provision for (benefit from) income taxes were as follows (in thousands):

	Year ended December 31,
	2020		2019		2018
Current:
Federal	$	—	$	—	$	—
State	2		7		324
Foreign	684		612		222
Deferred:
Federal	—		(966)		(307)
State	—		(198)		(52)
Foreign	—		—		—
Total income tax expense (benefit)	$	686	$	(545)	$	187

Reconciliation of Income Tax Provision (Benefit) Computed at the Statutory Federal Income Tax Rate to Effective Income Tax Rate (Provision) Benefit as Reflected in the Financial Statements

A reconciliation of income tax expense (benefit) computed at the statutory federal income tax rate to the Company’s effective income tax rate as reflected in the financial statements is as follows:

	Year ended December 31,
	2020		2019		2018
Federal income tax expense at statutory rate	21.0	%	21.0	%	21.0	%
State income tax, net of federal benefit	3.1	%	3.7	%	5.1	%
Permanent differences	(0.6)	%	(0.8)	%	(0.7)	%
Stock-based compensation	(2.4)	%	(0.7)	%	1.6	%
Research and development credit	6.0	%	5.4	%	6.5	%
Foreign differential	(4.6)	%	(3.7)	%	(4.4)	%
Federal tax rate change	—	%	—	%	0.1	%
Other	(0.3)	%	0.8	%	(0.1)	%
Change in valuation allowance	(22.3)	%	(25.6)	%	(29.1)	%
Effective income tax rate (expense) benefit	(0.1)	%	0.1	%	—	%

Components of Deferred Tax Assets and Liabilities

The significant components of the Company’s deferred tax assets and liabilities are composed of the following (in thousands):

	Year ended December 31,
	2020		2019
Deferred tax assets:
U.S. net operating loss carryforwards (federal and state)	$	546,098	$	439,839
Tax credit carryforwards (federal and state)	246,742		213,810
Capitalized license fees and research and development expenses	14,402		16,295
Deferred revenue	15,644		15,119
Stock-based compensation	51,828		46,111
Lease liabilities	48,680		52,631
Accruals and other	14,536		15,432
Total deferred tax assets	937,930		799,237
Intangible assets	(1,499)		(2,518)
Right-of-use assets	(45,976)		(49,480)
Fixed assets	(7,576)		(2,670)
Less valuation allowance	(882,879)		(744,569)
Net deferred taxes	$	—	$	—

Reconciliation of Unrecognized Tax Benefits

A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows (in thousands):

	Unrecognized tax benefits
Balance as of December 31, 2018	$	12,095
Increases (decreases) for tax positions related to current period	3,554
Increases (decreases) for tax positions related to prior periods	296
Balance as of December 31, 2019	15,945
Increases (decreases) for tax positions related to current period	3,149
Increases (decreases) for tax positions related to prior periods	(100)
Balance as of December 31, 2020	18,994