Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Taxes

Schedule of effective tax rates differing from U.S. federal statutory rate

	Year Ended December 31,
	2019				2018				2017
	(in thousands, except percentages)
U.S. federal taxes (benefit) at statutory rate	$	(25,794)	(21.00)	%	$	(26,800)	(21.00)	%	$	(46,206)	(34.00)	%
State tax expense		(6,607)	(5.38)	%		(4,468)	(3.50)	%		(6,559)	(4.83)	%
Research and development credits		(1,645)	(1.34)	%		(1,164)	(0.91)	%		(1,149)	(0.85)	%
Stock-based compensation		(7,544)	(6.14)	%		(3,148)	(2.47)	%		(5,036)	(3.71)	%
Change in federal tax rate		—	0.00	%		—	0.00	%		44,701	32.89	%
Mark to market fair value adjustments		—	0.00	%		865	0.68	%		(390)	(0.29)	%
Nondeductible settlement for claims		—	0.00	%		1	0.00	%		3,873	2.85	%
Foreign tax		1,612	1.31	%		195	0.15	%		153	0.11	%
Other nondeductible items		1,378	1.12	%		690	0.54	%		856	0.63	%
Change in valuation allowance		40,599	33.06	%		34,150	26.76	%		10,211	7.51	%
Provision for income taxes	$	1,999	1.63	%	$	321	0.25	%	$	454	0.31	%

Schedule of tax effects of temporary differences that give rise to significant portions of the deferred tax assets

	December 31,
	2019		2018
	(in thousands)
Deferred tax assets:
Net operating loss carryforwards	$	124,777	$	95,321
Research and development tax credit carryforwards		18,189		15,632
Reserves and accruals		10,002		7,839
Lease Liabilities		7,838		—
Deferred revenue		3,288		83
Stock-based compensation		6,106		4,076
Total deferred tax assets before valuation allowance		170,200		122,951
Less: valuation allowance		(163,040)		(122,441)
		7,160		510
Deferred tax liabilities:
Property and equipment		—		(510)
Right-of-use lease assets		(7,160)		—
Net deferred tax assets	$	—	$	—

Schedule of reconciliation of the beginning and ending amount of gross unrecognized tax benefits

	Year Ended December 31,
	2019		2018		2017
	(in thousands)
Balance at beginning of year	$	7,362	$	5,945	$	4,293
Additions based on tax positions related to the current year		1,426		1,416		1,651
Additions (reductions) for tax positions of prior years		(169)		1		1
Balance at end of year	$	8,619	$	7,362	$	5,945