Income Taxes (Tables)

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

Schedule of Reconciliation of the Company's Effective Tax Rate to the Statutory Federal Income Tax Rate

A reconciliation of the Company’s effective tax rate to the statutory federal income tax rate is as follows:

	Years Ended December 31,
	2020			2019
Federal income tax at statutory federal rate		21.0	%		21.0	%
State taxes		6.4			6.2
Permanent differences		—			(1.2	)
Tax credits		(0.1	)		0.7
Recapture of tax credits		34.9			—
Forfeiture of vested stock options		—			(24.8	)
Other		(3.2	)		0.2
Change in valuation allowance		(59.4	)		4.4
Total		(0.4	)%		6.5	%

Schedule of Temporary Differences That Give Rise to Significant Net Deferred Tax Assets

Temporary differences that give rise to significant net deferred tax assets as of December 31, 2020 and 2019 are as follows:

	December 31,
(in thousands)	2020			2019
Deferred tax assets
Net operating losses	$	61,905		$	61,189
Capitalized research and development expenses		423			564
Credit carryforwards		167,501			166,459
Deferred compensation		1,890			1,479
Election out of installment method		820			820
Accrued expenses		124			—
Other temporary differences		720			1,089
Installment sale tax basis		15,869			15,868
Total gross deferred tax assets		249,252			247,468
Valuation allowance		(249,252	)		(247,468	)

Schedule of Changes in the Valuation Allowance

The change in the valuation allowance against the deferred tax assets in the years ended December 31, 2020 and 2019 was as follows:

(in thousands)	Balance at Beginning of Period		Additions		Deductions			Balance at End of Period
December 31, 2019		248,478		—		(1,010	)		247,468
December 31, 2020		247,468		1,784		—			249,252