Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Schedule of components of loss before provision for income taxes

The components of loss before provision for income taxes were as follows (in thousands):

	Year Ended December 31,
	2018			2017			2016
	(in thousands)
United States	$	(84,313	)	$	(83,214	)	$	(46,133	)
Foreign	88			—			—
Total	$	(84,225	)	$	(83,214	)	$	(46,133	)

Schedule of components of the provision for income taxes

The components of the provision for income taxes are as follows:

	Year Ended December 31,
	2018		2017		2016
	(in thousands)
Current:
State	$	4	$	—	$	—
Foreign	34		7		6
Total current tax expense	38		7		6
Total provision for income taxes	$	38	$	7	$	6

Schedule of the components of deferred tax assets and liabilities

Significant components of the Company’s deferred tax assets are as follows:

	Year Ended December 31,
	2018			2017
	(in thousands)
Deferred tax assets:
Net operating losses carryforwards	$	36,783		$	25,657
Intangible assets	17,107			10,436
Accruals and reserves	5,127			3,553
Research and development credits	5,753			2,823
Stock-based compensation	1,289			727
Other	210			484
Total deferred tax asset	$	66,269		$	43,680
Deferred tax liabilities:
Property and equipment	$	(73	)	$	—
Less: valuation allowance	(66,196		)	(43,680		)
Net deferred tax assets	$	—		$	—

Effective tax rate reconciliation

The following table presents a reconciliation of the income tax expense computed at the statutory federal rate and the Company's income tax expense for the periods presented:

	Year Ended December 31,
	2018			2017			2016
	(in thousands)
Tax at the statutory federal rate	$	(17,690	)	$	(28,293	)	$	(15,687	)
Other nondeductible items	329			371			360
Stock-based compensation	497			3,819			413
Research and development credits	(1,726		)	(714		)	(304		)
Change in valuation allowance	22,516			5,415			16,640
State taxes, net of federal benefits	(4,231		)	(1,868		)	(1,224		)
Change in tax rate due to Tax Act	—			21,346			—
Other	343			(69		)	(192		)
Total provision for income taxes	$	38		$	7		$	6

Reconciliation of the balance of total gross unrecognized tax benefits

A reconciliation of the beginning and ending balance of total unrecognized tax benefits is as follows:

	Year Ended December 31,
	2018		2017		2016
	(in thousands)
Unrecognized tax benefits - Beginning of period	$	1,712	$	884	$	1,691
Increases related to current year’s tax positions	1,635		828		353
Increases related to prior years' tax positions	80		—		—
Decreases related to prior years’ tax positions	—		—		(1,160		)
Unrecognized tax benefits - End of period	$	3,427	$	1,712	$	884