Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Schedule of reconciliation of the statutory U.S. federal rate to the Company's effective tax rate

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

	Years ended December 31,
	2019		2018		2017
Percent of pre-tax income:
U.S. federal statutory income tax rate	21.0	%	21.0	%	35.0	%
State taxes, net of federal benefit	10.9	%	18.5	%	14.6	%
Permanent items	(1.0	)%	4.0	%	4.0	%
Remeasurement of deferred tax assets	—	%	—	%	49.9	%
Impact of state rate changes	0.1	%	(0.2	)%	(27.9	)%
Research and development credit	2.8	%	(2.4	)%	—	%
Alternative minimum tax credit	—	%	—	%	(1.3	)%
Change in valuation allowance	(33.6	)%	(42.6	)%	(78.6	)%
Effective income tax rate	0.2	%	(1.7	)%	(4.3	)%

Schedule of components of income tax (benefit) expense

The components of income tax benefit are as follows:

	Years ended December 31,
	2019			2018			2017
Current:
Federal	$	—		$	—		$	173
State	(111		)	(1,063		)	(1,356		)
Deferred:
Federal	—			—			(3,529		)
State	—			—			—
Income tax benefit	$	(111	)	$	(1,063	)	$	(4,712	)

Schedule of significant components of the Company's deferred tax assets (liabilities)

Significant components of the Company's deferred tax assets (liabilities) for 2019 and 2018 consist of the following:

	As of December 31,
	2019			2018
Deferred tax assets (liabilities)
License and technology payments	7,116			7,221
Share-based compensation	22,131			20,342
Accrued expenses	362			371
Right-of-use asset	(163		)	—
Lease obligation	162			—
Depreciation	(18		)	(28		)
Federal and state net operating loss carryforwards	105,375			88,766
Research and development credits	7,353			5,933
Other	6			5
Deferred income tax assets	142,324			122,610
Valuation allowance	(142,324		)	(122,610		)
Net deferred tax assets	$	—		$	—

Schedule of position with respect to uncertain tax positions

The Company's position with respect to uncertain tax positions is set forth below:

Opening balance	$	13,983
Gross amount of increases in unrecognized tax benefits during the period - current year provisions	—
Gross amount of increases in unrecognized tax benefits during the period - prior year provisions	18
Gross amount of decreases in unrecognized tax benefits during the period - other	(1,579		)
Decreases due to settlement with tax authorities during the period	(195		)
Reduction of unrecognized tax benefits due to expiration of the state of limitations during the period	—
Closing Balance	$	12,227