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Income Taxes - Reconciliation of Reported Estimated Income Tax Benefit (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
United States federal tax at statutory rate	$ (31,880)	$ (36,005)	$ (6,869)
State taxes (net of federal benefit)	(9,524)	(11,133)	(735)
Deferred income tax adjustments	2,004	(4,435)	607
Deferred state blended rate adjustments	0	0	(485)
Deferred federal rate change reduction in corporate rate	0	0	39,447
Research credit, net	(5,830)	(8,466)	(8,455)
Orphan drug credit, net	(301)	(872)	(1,853)
Other permanent items	1,206	148	276
Equity-based compensation	1,889	758	2,067
Change in valuation allowance	42,436	60,005	(24,000)
Income tax expense/(benefit)	$ 0	$ 0	$ 0

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to deferred tax adjustments.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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