Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Reconciliation of Federal Statutory Income Tax Rate

Reconciliation of the Federal statutory income tax rate of 21% to the effective rate is as follows:

	2018			2017			2016
Federal statutory income (benefit) tax rate		21.00	%		(34.00	%)		34.00	%
2017 Tax Act, net deferred tax remeasurement		—			(626.73	)		—
State taxes, net of federal benefit		(0.11	)		(2.01	)		2.88
Stock compensation		(4.74	)		(5.18	)		(0.61	)
Permanent differences-other		(1.33	)		(13.39	)		(1.00	)
North Carolina tax rate change		—			(32.75	)		—
Research and development (“R&D”) credit		—			5.54			0.98
Valuation release for bargain purchase gain		—			(302.23	)		—
Other		(2.07	)		(1.36	)		(0.47	)
Decrease (increase) in valuation allowance		(12.65	)		709.88			(35.78	)
		0.10	%		(302.23	%)		0.00	%

Significant Components of Deferred Tax Assets and Liabilities

The tax effects of temporary differences and net operating losses that give rise to significant components of deferred tax assets and liabilities consist of the following:

	December 31,
Deferred tax assets (liabilities)	2018			2017
Deferred revenue	$	—		$	—
Basis difference in equipment		(459	)		(587	)
Basis difference in intangibles		(6,045	)		(8,288	)
Accrued liabilities and other		2,246			654
R&D credit		10,980			11,882
AMT credit		—			79
Stock options		4,360			6,115
Net operating loss carry-forward		64,376			61,660
		75,458			71,515
Less: valuation allowance		(75,458	)		(71,515	)
	$	—		$	—