Income Taxes Income Taxes (Tables)

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

Schedule of Deferred Tax Assets and Liabilities

The following table represents the significant components of our deferred tax assets and liabilities for the periods presented:

	December 31,
	2020		2019
Deferred income tax assets
Net operating loss carryforwards	$	57,763	$	49,211
Tax credit carryforwards	12,422		8,638
Stock-based compensation	6,011		5,142
Compensation accruals	7,026		2,297
Lease liability	17,540		18,404
Accruals and reserves	2,079		795
Gross deferred income tax assets	102,841		84,487
Valuation allowance	(44,307)		(62,274)
Total deferred income tax assets, net of valuation allowance	58,534		22,213
Deferred income tax liabilities
Intangible assets	(514)		(605)
Prepaid expenses	—		(1,688)
Convertible senior notes	(45,616)		(5,359)
Right-of-use assets	(12,404)		(13,579)
Fixed assets	—		(982)
Total deferred income tax liabilities	(58,534)		(22,213)
Net deferred income tax assets and liabilities	$	—	$	—

Summary of Operating Loss Carryforwards

The following table represents our net operating loss ("NOL") carryforwards as of December 31, 2020 and 2019:

	December 31,
	2020		2019
Federal	$	227,751	$	195,133
Various states	12,576		10,421
Foreign	2,050		1,212

Schedule of Effective Income Tax Rate Reconciliation

The following table is a reconciliation of the U.S. federal income tax at statutory rate to our effective income tax rate:

	December 31,
	2020		2019		2018
U.S. federal income tax at statutory rate	21.00	%	21.00	%	21.00	%
State taxes (net of federal benefit)	25.23		4.71		5.67
Stock-based compensation	69.14		1.20		7.51
Permanent differences	(1.03)		(0.97)		(0.57)
Federal research and development credit	20.42		2.45		4.26
Change in valuation allowance	(132.88)		(29.73)		(37.33)
Other	1.32		1.34		(0.54)
Extinguishment of 2023 Notes	(3.20)		—		—
Effective income tax rate	—	%	—	%	—	%

Schedule of Unrecognized Tax Benefits Roll Forward

The following table summarizes the activity related to unrecognized tax benefits:

	December 31,
	2020		2019
Unrecognized benefit—beginning of year	$	2,159	$	1,663
Gross decreases—prior year tax positions	—		(127)
Gross increases—current year tax positions	946		623
Unrecognized benefit—end of year	$	3,105	$	2,159