Income Taxes - Reconciliation (Details)	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Federal statutory tax rate	21.00%	21.00%	35.00%
State income taxes, net of federal benefit	2.00%	1.00%	3.00%
Tax benefit on stock option exercises, net of forfeitures	1.00%	(11.00%)	(4.00%)
R&D tax credits and Orphan Drug credits	(2.00%)	(7.00%)	(10.00%)
Limitation on executive compensation	10.00%	3.00%
Revaluation of net deferred tax assets due to U.S. tax reform	0	0	0.05
Change in valuation allowance	4.00%	0.00%	0.00%
Other	(1.00%)	(1.00%)	0.00%
Effective tax rate	35.00%	6.00%	29.00%

Effective Income Tax Rate Reconciliation, Limitation On Executive Compensation, Percent

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Effective Income Tax Rate Reconciliation, Stock Options Exercised, Tax Benefit

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

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage 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 changes in the valuation allowance for deferred tax assets.

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Percentage 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 applicable to state and local income tax expense (benefit), net of federal tax expense (benefit).

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Percentage 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 tax credits. Including, but not limited to, research credit, foreign tax credit, investment tax credit, and other tax credits.

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Percentage of reported income tax expense (benefit) in excess of (less than) expected income tax expense (benefit) computed by applying domestic federal statutory income tax rate to pretax income (loss) from continuing operations, attributable to Tax Cuts and Jobs Act.

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