Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Components of Income Tax (Benefit) Expense

The Company’s loss before tax is only attributable to U.S. operations. The components of the income tax (benefit) expense are as follows (in thousands):

	Year Ended December 31,
	2019		2018		2017
Current (benefit from) provision for income taxes:
Federal	$	—	$	—	$	—
State		—		—		—
Total current (benefit from) provision for income    taxes		—		—		—
Deferred (benefit from) provision for income taxes:		—		—		—
Federal		—		—		—
State		—		—		—
Total deferred tax (benefit from) provision for    income taxes		—		—		—
(Benefit from) provision for income taxes	$	—	$	—	$	—

Reconciliation of the Federal Statutory Income Tax Rate to the Company's Effective Income Tax Rate

A reconciliation of the federal statutory income tax rate to the Company’s effective income tax rate is as follows:

	Year Ended December 31,
	2019			2018			2017
Federal statutory income tax rate		(21.0	%)		(21.0	%)		34.0	%
Permanent items		1.3			1.6			5.5
Excess tax benefit for stock-based compensation	(13.3)			(2.8)			(2.0)
Tax credits	(38.3)			(3.5)			(7.2)
Change in valuation allowance		70.3			24.5		(224.1)
Change in tax rate		—			—		193.8
Other		1.0			1.2			—
(Benefit from) provision for income taxes		—	%		—	%		—	%

Tax Effects of Temporary Differences and Carryforwards that Give Rise to Significant Portions of the Deferred Tax Assets

13. Income Taxes (continued)

The tax effects of temporary differences and carryforwards that give rise to significant portions of the deferred tax assets consist of the following (in thousands):

	December 31,
	2019			2018
Deferred tax assets:
Net operating loss carryforwards	$	76,033		$	62,405
Tax credits		39,625			11,794
Amortization of deferred stock compensation - non-    qualified		5,172			6,569
Reserves and accruals		1,528			1,140
Deferred revenue		20,312			20,991
Depreciation and amortization		15			—
Lease liability		434			—
Gross deferred tax assets		143,119			102,899
Less: valuation allowance		(142,761	)		(102,891	)
Total deferred tax assets		358			8
Deferred tax liabilities:
Depreciation and amortization		—			(8	)
Right of use asset		(358	)		—
Total deferred tax liabilities		(358	)		(8	)
Net deferred tax assets	$	—		$	—

Reconciliation of the Company's Unrecognized Tax Benefits

13. Income Taxes (continued)

A reconciliation of the Company’s unrecognized tax benefits for the years ended December 31, 2019, 2018 and 2017, is as follows (in thousands):

	Unrecognized Income Tax Benefits
Balance as of December 31, 2017	$	8,786
Additions for current tax positions		928
Balance as of December 31, 2018		9,714
Additions for current tax positions		3,455
Additions for prior tax positions		12,090
Balance as of December 31, 2019	$	25,259