Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Schedule of Components of Income Tax Expense (Benefit)

The components of income before taxes are as follows (in thousands):

	Year Ended December 31,
	2017			2018
United States	$	(22,358	)	$	(37,630	)
International	—			—
	$	(22,358	)	$	(37,630	)

Schedule of Effective Income Tax Rate Reconciliation

A reconciliation of the statutory U.S. federal rate to the Company’s effective tax rate is as follows (in thousands):

	Year Ended December 31,
	2017			2018
Tax at federal statutory rate	$	(7,602	)	$	(7,902	)
State taxes, net of federal benefit	(1,155		)	(1,582		)
Permanent differences	535			289
Loss on Series C warrant liability	—			2,500
Tax Cut and Jobs Act	12,456			—
Change in valuation allowance	(3,832		)	6,197
General business credits	(465		)	136
Other	69			376
Provision for taxes	$	6		$	14

Schedule of Deferred Tax Assets and Liabilities

Significant components of the Company’s net deferred tax assets as of December 31, 2017 and 2018 consist of the following (in thousands):

	December 31,
	2017			2018
Deferred tax assets:
Net operating loss carryforwards	$	28,056		$	33,815
Research and development credits	5,081			4,944
Capitalized start-up costs/Intangibles	19			16
Accruals and reserves	705			1,169
Property and equipment	44			82
Stock-based compensation	197			274
Total deferred tax assets	34,102			40,300
Less: Valuation allowance	(34,102		)	(40,300		)
Net deferred tax assets	$	—		$	—

Reconciliation of Unrecognized Tax Benefits

A reconciliation of the unrecognized tax benefits from January 1, 2017 to December 31, 2018 is as follows (in thousands):

	December 31,
	2017		2018
Balance at the beginning of year	$	551	$	615
Increases related to current years’ tax positions	64		118
Increases/(decreases) related to prior years’ tax positions	—		615
Balance at end of year	$	615	$	1,348