Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

Income Taxes [Abstract]

Income Tax Expense (Benefit)

The income tax provision is comprised of the following:

	Year Ended December 31, 2018			Year Ended December 31, 2017			Year Ended December 31, 2016
Current:
Federal	$	—		$	—		$	—
State		(3	)		(3	)		(133	)
Foreign		—			—			—
		(3	)		(3	)		(133	)
Deferred:
Federal		—			—			—
State		—			—			—
Total income tax provision	$	(3	)	$	(3	)	$	(133	)

Effective Income Tax Rate Reconciliation

A reconciliation of the United States federal statutory income tax rate to our effective income tax rate is as follows:

	Year Ended December 31, 2018			Year Ended December 31, 2017			Year Ended December 31, 2016
United States federal statutory rate		21.00	%		35.00	%		35.00	%
State taxes, net of federal benefit		(0.01	)%		(0.01	)%		(0.31	)%
Valuation allowance		(24.33	)%		(35.94	)%		(35.43	)%
Accounting method change  -  ASC 606		2.07	%		—			—
R&D Credit		1.53	%		1.43	%		0.66	%
Other		(0.27	)%		(0.50	)%		(0.39	)%
Effective income tax rate		(0.01	)%		(0.02	)%		(0.47	)%

Deferred Tax Assets and Liabilities

Deferred tax assets (liabilities) consist of the following:

	Year Ended December 31, 2018			Year Ended December 31, 2017
Deferred tax assets:
Reserves and accruals	$	45		$	963
Research and development credits and other credits		1,635			1,300
Net operating loss carry forward		25,733			22,448
Stock based compensation		8,857			9,260
Other		26			54
Total deferred tax assets		36,296			34,025
Valuation allowance		(36,296	)		(34,025	)
Deferred tax assets after valuation allowance		—			—
Deferred tax liability:
Depreciation and amortization		—			—
Total deferred tax liability		—			—
Net deferred tax assets	$	—		$	—

Unrecognized Tax Benefits Reconciliation

A reconciliation of beginning and ending amounts of unrecognized tax benefits follows:

	Year Ended December 31, 2018		Year Ended December 31, 2017		Year Ended December 31, 2016
Balance at the beginning of the year	$	316	$	316	$	316
Additions based on tax positions related to the current year		—		—		—
Additions for tax positions of prior years		—		—		—
Settlements		—		—		—
Lapse of applicable statute of limitations		—		—		—
Balance at the end of the year	$	316	$	316	$	316