Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Components of Income Taxes (Benefit)

The Company’s benefit from income taxes is as follows:

	December 31,
	2018			2017			2016
Current:
Federal	$	—		$	—		$	—
State		(389	)		(204	)		(468	)
		(389	)		(204	)		(468	)
Deferred:
Federal		—			—			—
State		—			—			—
		—			—			—
Benefit from income taxes	$	(389	)	$	(204	)	$	(468	)

Schedule of Reconciliation of Income Taxes Computed Using U.S. Federal Statutory Rate to that Reflected in Operations

A reconciliation of income taxes computed using the U.S. federal statutory rate to that reflected in operations is as follows:

	December 31,
	2018			2017			2016
Income taxes using U.S. federal statutory rate		21.00	%		34.00	%		34.00	%
State income taxes, net of federal benefit		6.82	%		5.33	%		5.44	%
Tax Cuts and Jobs Act		0.00	%		-44.43	%		0.00	%
Impact of R&D tax credit on effective tax rate		3.48	%		3.25	%		3.24	%
Stock option shortfalls and cancellations		-0.43	%		0.21	%		-0.07	%
Permanent items and other		-0.15	%		-0.56	%		-0.64	%
Change in valuation allowance		-31.76	%		2.55	%		-41.17	%
Provision to return		0.03	%		0.00	%		0.00	%
Non-taxable revenue		1.54	%		0.00	%		0.00	%
		0.53	%		0.35	%		0.80	%

Schedule of Significant Components of Company's Deferred Tax Assets and Liabilities

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

	December 31,
	2018			2017
Deferred tax assets:
Net operating loss carryforwards	$	73,578		$	54,831
Federal and state tax credits		11,108			8,401
Deferred revenue		1,111			—
Stock-based compensation expense		3,605			2,382
Other		420			582
		89,822			66,196
Deferred tax liabilities:
Accelerated depreciation		(7	)		(23	)
Valuation allowance		(89,815	)		(66,173	)
Net deferred tax asset	$	—		$	—