Income taxes (Tables)

12 Months Ended

Dec. 31, 2020

Income taxes

Schedule of components of income expense (benefit)

	Year ended December 31,
	2020		2019		2018
	(in thousands)
Current
Federal	$	—	$	—	$	180
State		—		—		—
Total current		—		—		180
Deferred
Federal		—		—		—
State		—		—		—
Total deferred		—		—		—
Total tax expense	$	—	$	—	$	180

Schedule of reconciliation of the expected income tax (benefit) computed using the federal statutory income tax rate to the effective income tax rate

	Year ended December 31,
	2020			2019			2018
Income tax computed at federal statutory tax rate		21.0	%		21.0	%		21.0	%
Non-deductible expenses		5.0	%		(2.2)	%		(2.1)	%
Other		1.9	%		—	%		—	%
State taxes, net of federal benefit		(2.3)	%		8.0	%		6.3	%
Change in valuation allowance		(5.0)	%		(36.2)	%		(28.1)	%
General business credit carryovers		(20.6)	%		9.4	%		3.1	%
Total		—	%		—	%		0.2	%

Schedule of principal components of the Company's deferred tax assets and liabilities

	As of December 31,
	2020		2019
	(in thousands)
Deferred tax assets:
Net operating loss carryforwards	$	41,130	$	49,713
Tax credit carryforwards		28,173		17,297
Deferred revenue		12,176		16,805
Lease liability		13,006		9,335
Stock compensation		4,368		5,157
Non-deductible accruals and reserves		1,288		1,502
Intangibles		721		776
Total deferred tax assets		100,862		100,585
Less valuation allowance		(84,866)		(90,920)
Net deferred tax assets		15,996		9,665
Deferred tax liabilities
Unrealized gain on available-for-sale securities		(8)		(8)
Right of use assets		(9,852)		(7,779)
Depreciation and amortization		(6,136)		(1,878)
Net deferred taxes	$	—	$	—