Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Schedule of Reconciliation of the U.S. Federal Statutory Rate to the Company's Effective Tax Rate

The reconciliation of the U.S. federal statutory rate to the Company’s effective tax rate is as follows:

	Year Ended December 31,
	2019			2018			2017
Tax at statutory rates		21.0	%		21.0	%		35.0	%
State income taxes		2.6			3.6			6.5
Permanent differences		(1.2	)		(0.6	)		(2.5	)
Research and development credits		1.0			1.0			1.5
US tax rate change		—			-			(52.7	)
Change in valuation allowance		(23.4	)		(25.0	)		12.2
Effective tax rate		0.0	%		0.0	%		0.0	%

Schedule Of Deferred Tax Assets

The significant components of the Company’s deferred tax asset consist of the following at December 31, 2019 and 2018 (in thousands):

	December 31,
	2019			2018
Deferred tax assets:
Net operating loss carryforwards	$	86,990		$	73,612
Tax credits		8,329			7,603
Other temporary differences		2,888			3,156
Start-up expenditures		2,716			3,026
Stock option expenses		3,450			3,130
Lease liability		987			—
Total deferred tax assets		105,360			90,527
Deferred tax asset valuation allowance		(104,204	)		(90,361	)
Net deferred tax assets		1,156			166
Deferred tax liabilities:
Right of use asset		(859	)		—
Prepaid expenses		(297	)		(166	)
Net deferred taxes	$	—		$	—