Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Components of the Company's Deferred Tax Assets

The significant components of the Company's deferred tax assets are comprised of the following (in thousands):



	Year Ended December 31,
	2019			2018
Deferred tax assets:
U.S. and state net operating loss carryforwards	$	184,355		$	149,170
Research and development credits	21,345			16,340
Stock compensation	14,024			13,819
Lease liabilities	7,090			—
Accruals and other temporary differences	5,584			3,626
Total deferred tax assets	232,398			182,955
Right of use asset	(6,429		)	—
Less valuation allowance	(225,969		)	(182,955		)
Net deferred tax assets	$	—		$	—

Schedule of Effective Income Tax Rate Reconciliation

A reconciliation of income tax expense computed at the statutory federal income tax rate to income taxes as reflected in the consolidated financial statements is as follows:



	Year Ended December 31,
	2019		2018		2017
Federal income tax expense at statutory rate	21.0	%	21.0	%	34.0	%
State income tax, net of federal benefit	9.9	%	7.0	%	5.6	%
Permanent differences	0.2	%	2.0	%	1.9	%
Research and development credit	4.2	%	3.2	%	1.9	%
Tax reform rate change	—	%	—	%	(54.7	)%
Other	(0.9	)%	(0.6	)%	(0.3	)%
Change in valuation allowance	(34.4	)%	(32.6	)%	11.6	%
Effective income tax rate	—	%	—	%	—	%