Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

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,
	2018			2017
Federal income tax at statutory federal rate		21.0	%		35.0	%
State taxes		6.2			1.7
Permanent differences		(0.1	)		(3.0	)
Stock-based compensation		(0.4	)		(7.2	)
Tax Cuts and Jobs Act Impact		0.1			(19.9	)
Tax credits		2.5			11.6
Change in deferred state tax rate		—			7.7
Other		—			0.3
Change in valuation allowance		(18.1	)		9.9
Total		11.2	%		36.1	%

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, 2018 and 2017 are as follows:

	December 31,
(in thousands)	2018			2017
Deferred tax assets
Net operating losses	$	54,407		$	43,133
Capitalized research and development expenses		705			847
Credit carryforwards		166,367			164,709
Depreciation		2,725			2,605
Deferred compensation		6,315			5,855
Accrued expenses		655			905
Other temporary differences		2,423			2,145
Installment sale tax basis		14,881			15,868
Total gross deferred tax assets		248,478			236,067
Valuation allowance		(248,478	)		(236,067	)

Schedule of Changes in the Valuation Allowance

The change in the valuation allowance against the deferred tax assets in the years ended December 31, 2018 and 2017 was as follows:

(in thousands)	Balance at Beginning of Period		Additions		Deductions			Balance at End of Period
December 31, 2017	$	414,558	$	66,801	$	(245,292	)	$	236,067
December 31, 2018		236,067		12,411		—			248,478