Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Schedule of Reconciliation between Statutory Federal Income Tax Rate and Effective Tax Rate

The following is the reconciliation between the statutory federal income tax rate and the Company’s effective tax rate:  

	Year Ended December 31,
	2018			2017			2016
				As revised (Note 2)
Federal statutory income tax rate		21.0	%		34.0	%		34.0	%
State taxes (tax effected)		8.6			7.1			8.4
Non-deductible expenses and other		2.5			2.0			(12.9	)
Research and development credits		5.9			6.0			17.8
Tax Act – net deferred tax rate change		—			(25.1	)		—
Change in valuation allowance		(38.0	)		(24.0	)		(47.3	)
Total		—	%		—	%		—	%

Components of Company's Deferred Tax Assets

As of December 31, 2018 and 2017, the components of the Company’s deferred tax assets are as follows (in thousands):

	As of December 31,
	2018			2017
				As revised (Note 2)
Deferred tax assets:
Net operating loss carryforwards	$	49,689		$	22,246
Research and development credits carryforwards		12,908			8,631
Stock-based compensation		4,349			890
Deferred revenue		—			9,391
Start-up costs		1,237			1,354
Depreciation		(959	)		(457	)
Other		1,858			1,327
Total deferred tax assets		69,082			43,382
Less: valuation allowance		(69,082	)		(43,382	)
Net deferred tax assets	$	—		$	—

Schedule of Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits

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

	For the Year Ended December 31,
	2018		2017			2016
			As revised (Note 2)
Beginning balance	$	2,471	$	1,474		$	719
Increases (decreases) of unrecognized tax benefits related to prior year		289		(97	)		—
Increases of unrecognized tax benefits related to current year		1,050		1,094			755
Ending balance	$	3,810	$	2,471		$	1,474