Income Taxes	3 Months Ended
Mar. 31, 2018
Income Taxes
Income Taxes	11. Income Taxes On December 22, 2017, the Tax Cuts and Jobs Act (the TCJA), which significantly modified U.S. corporate income tax law, was signed into law by President Trump. The TCJA contains significant changes to corporate income taxation, including but not limited to the reduction of the corporate income tax rate from a top marginal rate of 35% to a flat rate of 21%, limitation of the tax deduction for interest expense to 30% of earnings (except for certain small businesses), limitation of the deduction for net operating losses to 80% of current year taxable income and generally eliminating net operating loss carrybacks, allowing net operating losses to carryforward without expiration, one-time taxation of offshore earnings at reduced rates regardless of whether they are repatriated, elimination of U.S. tax on foreign earnings (subject to certain important exceptions), immediate deductions for certain new investments instead of deductions for depreciation expense over time, and modifying or repealing many business deductions and credits (including changes to the orphan drug tax credit and changes to the deductibility of research and experimental expenditures that will be effective in the future). Notwithstanding the reduction in the corporate income tax rate, the overall impact of the new federal tax law is uncertain, including to what extent various states will conform to the newly enacted federal tax law. The Company has recorded the necessary provisional adjustments in the financial statements in accordance with its current understanding of the TCJA and guidance currently available as of this filing and recorded a provisional reduction of $6.8 million to its gross deferred tax assets in the fourth quarter of 2017, the period in which the legislation was enacted. The provisional reduction was fully offset by an equal reduction in the Company’s valuation allowance given the Company’s historical net losses, resulting in no net income tax expense being recorded. The Company may adjust these provisional amounts in future periods if its interpretation of the TCJA changes or as additional guidance becomes available. Any subsequent adjustment to these amounts is not expected to have a significant impact due to the valuation allowance. The effective tax rate for the three months ended March 31, 2018 and 2017 was zero percent. As a result of the analysis of all available evidence as of March 31, 2018 and December 31, 2017, the Company recorded a full valuation allowance on its net deferred tax assets. Consequently, the Company reported no income tax benefit for the three month periods ended March 31, 2018 and 2017. If the Company’s assumptions change and the Company believes that it will be able to realize these deferred tax assets, the tax benefits relating to any reversal of the valuation allowance on deferred tax assets will be recognized as a reduction of future income tax expense. If the assumptions do not change, each period the Company could record an additional valuation allowance on any increases in the deferred tax assets.

11. Income Taxes

On December 22, 2017, the Tax Cuts and Jobs Act (the TCJA), which significantly modified U.S. corporate income tax law, was signed into law by President Trump. The TCJA contains significant changes to corporate income taxation, including but not limited to the reduction of the corporate income tax rate from a top marginal rate of 35% to a flat rate of 21%, limitation of the tax deduction for interest expense to 30% of earnings (except for certain small businesses), limitation of the deduction for net operating losses to 80% of current year taxable income and generally eliminating net operating loss carrybacks, allowing net operating losses to carryforward without expiration, one-time taxation of offshore earnings at reduced rates regardless of whether they are repatriated, elimination of U.S. tax on foreign earnings (subject to certain important exceptions), immediate deductions for certain new investments instead of deductions for depreciation expense over time, and modifying or repealing many business deductions and credits (including changes to the orphan drug tax credit and changes to the deductibility of research and experimental expenditures that will be effective in the future). Notwithstanding the reduction in the corporate income tax rate, the overall impact of the new federal tax law is uncertain, including to what extent various states will conform to the newly enacted federal tax law.

The Company has recorded the necessary provisional adjustments in the financial statements in accordance with its current understanding of the TCJA and guidance currently available as of this filing and recorded a provisional reduction of $6.8 million to its gross deferred tax assets in the fourth quarter of 2017, the period in which the legislation was enacted. The provisional reduction was fully offset by an equal reduction in the Company’s valuation allowance given the Company’s historical net losses, resulting in no net income tax expense being recorded. The Company may adjust these provisional amounts in future periods if its interpretation of the TCJA changes or as additional guidance becomes available. Any subsequent adjustment to these amounts is not expected to have a significant impact due to the valuation allowance.

The effective tax rate for the three months ended March 31, 2018 and 2017 was zero percent. As a result of the analysis of all available evidence as of March 31, 2018 and December 31, 2017, the Company recorded a full valuation allowance on its net deferred tax assets. Consequently, the Company reported no income tax benefit for the three month periods ended March 31, 2018 and 2017. If the Company’s assumptions change and the Company believes that it will be able to realize these deferred tax assets, the tax benefits relating to any reversal of the valuation allowance on deferred tax assets will be recognized as a reduction of future income tax expense. If the assumptions do not change, each period the Company could record an additional valuation allowance on any increases in the deferred tax assets.