Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Components of Income Taxes (Benefit)

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

	December 31,
	2017			2016			2015
Current:
Federal	$	—		$	—		$	—
State		(204	)		(468	)		(397	)
		(204	)		(468	)		(397	)
Deferred:
Federal	—			—			—
State	—			—			—
	—			—			—
Benefit from income taxes	$	(204	)	$	(468	)	$	(397	)

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,
	2017			2016			2015
Income taxes using U.S. federal statutory rate		34.00	%		34.00	%		34.00	%
State income taxes, net of federal benefit		5.33	%		5.44	%		5.95	%
Tax Cuts and Jobs Act		-44.43	%		0.00	%		0.00	%
Impact of R&D tax credit on effective tax rate		3.25	%		3.24	%		3.14	%
Stock option shortfalls and cancellations		0.21	%		-0.07	%		-0.03	%
Permanent items and other		-0.56	%		-0.64	%		-0.41	%
Change in valuation allowance		2.55	%		-41.17	%		-41.07	%
		0.35	%		0.80	%		1.58	%

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,
	2017			2016
Deferred tax assets:
Net operating loss carryforwards	$	54,831		$	57,887
Federal and state tax credits		8,401			6,221
Accelerated depreciation		-			259
Stock-based compensation expense		2,382			1,783
Other		582			641
		66,196			66,791
Deferred tax liabilities:
Accelerated depreciation		(23	)		-
Valuation allowance		(66,173	)		(66,791	)
Net deferred tax asset	$	—		$	—