Income Taxes	9 Months Ended
Sep. 30, 2020
Income Tax Disclosure [Abstract]
Income Taxes	Income TaxesFor the three months ended September 30, 2020 and 2019, the Company recorded income tax expense of $2.5 million and income tax benefit of $88.1 million, respectively. For the nine months ended September 30, 2020 and 2019, the Company recorded income tax expense of $5.6 million and income tax benefit of $88.1 million, respectively. The income tax expense for the three and nine months ended September 30, 2020 was primarily driven by the estimated effective tax rate for the year and the discrete impact of net shortfall tax expense related to stock-based compensation activity. The income tax benefit for the three and nine months ended September 30, 2019 was primarily due to the reduction of the Company's tax valuation allowance against substantially all of its deferred tax assets in the U.S. recognized during the three months ended September 30, 2019. Net income tax benefit of $1.6 million was also recorded during the three and nine months ended September 30, 2019 related to the generation of 2019 research and development and orphan drug credits, partially offset by current taxes payable to certain U.S. state and foreign jurisdictions and uncertain tax positions.The Company assesses the need for a valuation allowance against its deferred tax asset each quarter through the review of all available positive and negative evidence. Deferred tax assets are reduced by a tax valuation allowance when, in the opinion of management, it is more likely than not that some portion of the deferred tax assets will not be realized. The analysis depends on historical and projected taxable income. Projected taxable income includes significant assumptions related to revenue, commercial expenses and research and development activities. During the third quarter of 2019, after considering all available positive and negative evidence, including but not limited to cumulative income in recent periods, historical, current and future projected results and significant risks and uncertainties related to forecasts, the Company concluded that it was more likely than not that substantially all of its deferred tax assets in the U.S. are realizable in future periods. A valuation allowance was retained against certain District of Columbia state deferred tax assets as of September 30, 2020 and December 31, 2019.

Income Taxes

9 Months Ended

Sep. 30, 2020

Income TaxesFor the three months ended September 30, 2020 and 2019, the Company recorded income tax expense of $2.5 million and income tax benefit of $88.1 million, respectively. For the nine months ended September 30, 2020 and 2019, the Company recorded income tax expense of $5.6 million and income tax benefit of $88.1 million, respectively. The income tax expense for the three and nine months ended September 30, 2020 was primarily driven by the estimated effective tax rate for the year and the discrete impact of net shortfall tax expense related to stock-based compensation activity. The income tax benefit for the three and nine months ended September 30, 2019 was primarily due to the reduction of the Company's tax valuation allowance against substantially all of its deferred tax assets in the U.S. recognized during the three months ended September 30, 2019. Net income tax benefit of $1.6 million was also recorded during the three and nine months ended September 30, 2019 related to the generation of 2019 research and development and orphan drug credits, partially offset by current taxes payable to certain U.S. state and foreign jurisdictions and uncertain tax positions.The Company assesses the need for a valuation allowance against its deferred tax asset each quarter through the review of all available positive and negative evidence. Deferred tax assets are reduced by a tax valuation allowance when, in the opinion of management, it is more likely than not that some portion of the deferred tax assets will not be realized. The analysis depends on historical and projected taxable income. Projected taxable income includes significant assumptions related to revenue, commercial expenses and research and development activities. During the third quarter of 2019, after considering all available positive and negative evidence, including but not limited to cumulative income in recent periods, historical, current and future projected results and significant risks and uncertainties related to forecasts, the Company concluded that it was more likely than not that substantially all of its deferred tax assets in the U.S. are realizable in future periods. A valuation allowance was retained against certain District of Columbia state deferred tax assets as of September 30, 2020 and December 31, 2019.