Income Taxes	6 Months Ended
Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes Income Tax Provision The Company's income tax provision for quarterly interim periods is based on an estimated annual effective income tax rate calculated separately from the effect of significant, infrequent, or unusual items. The total income tax provision, including discontinued operations, was a tax expense of $1.0 million and $109.0 million for the three and six months ended March 31, 2018, respectively, compared to an income tax benefit of $4.5 million and $7.1 million for the three and six months ended March 31, 2017, respectively. The current fiscal year income tax expense was primarily driven by (1) the remeasurement of our deferred tax assets as a result of the enactment of the Tax Cuts and Jobs Act (Tax Act); and (2) several discrete tax expenses, including the impacts to our stock-based compensation expense as a result of current period activity; both partially offset by (3) the loss incurred from continuing operations; and (4) the completion of work necessary to claim an additional $2.3 million in tax credits related to prior fiscal years. The tax benefit for the six months ended March 31, 2017 was primarily driven by the Company's loss from continuing operations and the completion of work necessary to claim an additional $1.3 million in tax credits, which were recorded in fiscal 2017 but related to fiscal 2016. Deferred Tax Assets and Liabilities The Tax Act is comprehensive tax reform legislation that was enacted by the U.S. government on December 22, 2017. The Tax Act includes significant changes to the Internal Revenue Code, including a reduction in the corporate tax rate from 35% to 21%. Additionally, the Tax Act establishes new laws that will impact our fiscal 2019, including, but not limited to, eliminating the corporate alternative minimum tax (AMT), changes to how existing AMT credits can be realized, and imposing new limitations on the deductibility of certain executive compensation. In connection with our initial analysis of the Tax Act's impacts, and in accordance with the guidance in SAB 118, we recorded a discrete net tax expense of $112.6 million during the three months ended December 31, 2017. This net expense is primarily related to the corporate tax rate reduction and the associated remeasurement of our deferred tax assets. While a provisional tax expense of $112.6 million was recorded based on reasonable estimates of the impact of the reduction in the corporate tax rate, the estimate may be affected by additional analyses related to the Tax Act and temporary differences that will reverse during our fiscal 2018 and subsequent tax years. No change to the estimate was recorded during the three months ended March 31, 2018. The Company continues to evaluate its deferred tax assets each period to determine if a valuation allowance is required based on whether it is more likely than not that some portion of these deferred tax assets will not be realized. As of March 31, 2018, we concluded that it is more likely than not that a substantial portion of our deferred tax assets will be realized. As part of our analysis, we considered both positive and negative factors that impact profitability and whether those factors would lead to a change in the estimate of our deferred tax assets that may be realized in the future. Although the Tax Act may result in changes to our taxable income in the future, we do not anticipate that these changes would be significant enough to result in a change to our estimate when taken into account with other applicable factors. As of March 31, 2018, our conclusions on the valuation allowance and Internal Revenue Code Section 382 limitations related to our deferred tax assets remain consistent with the determinations we made during the period ended September 30, 2017, and such conclusions are based on similar company specific and industry factors to those discussed in Note 13 to the audited consolidated financial statements within our 2017 Annual Report.

Income Taxes

Income Tax Provision

The Company's income tax provision for quarterly interim periods is based on an estimated annual effective income tax rate calculated separately from the effect of significant, infrequent, or unusual items. The total income tax provision, including discontinued operations, was a tax expense of $1.0 million and $109.0 million for the three and six months ended March 31, 2018, respectively, compared to an income tax benefit of $4.5 million and $7.1 million for the three and six months ended March 31, 2017, respectively. The current fiscal year income tax expense was primarily driven by (1) the remeasurement of our deferred tax assets as a result of the enactment of the Tax Cuts and Jobs Act (Tax Act); and (2) several discrete tax expenses, including the impacts to our stock-based compensation expense as a result of current period activity; both partially offset by (3) the loss incurred from continuing operations; and (4) the completion of work necessary to claim an additional $2.3 million in tax credits related to prior fiscal years. The tax benefit for the six months ended March 31, 2017 was primarily driven by the Company's loss from continuing operations and the completion of work necessary to claim an additional $1.3 million in tax credits, which were recorded in fiscal 2017 but related to fiscal 2016.

Deferred Tax Assets and Liabilities

The Tax Act is comprehensive tax reform legislation that was enacted by the U.S. government on December 22, 2017. The Tax Act includes significant changes to the Internal Revenue Code, including a reduction in the corporate tax rate from 35% to 21%. Additionally, the Tax Act establishes new laws that will impact our fiscal 2019, including, but not limited to, eliminating the corporate alternative minimum tax (AMT), changes to how existing AMT credits can be realized, and imposing new limitations on the deductibility of certain executive compensation.

In connection with our initial analysis of the Tax Act's impacts, and in accordance with the guidance in SAB 118, we recorded a discrete net tax expense of $112.6 million during the three months ended December 31, 2017. This net expense is primarily related to the corporate tax rate reduction and the associated remeasurement of our deferred tax assets. While a provisional tax expense of $112.6 million was recorded based on reasonable estimates of the impact of the reduction in the corporate tax rate, the estimate may be affected by additional analyses related to the Tax Act and temporary differences that will reverse during our fiscal 2018 and subsequent tax years. No change to the estimate was recorded during the three months ended March 31, 2018.

The Company continues to evaluate its deferred tax assets each period to determine if a valuation allowance is required based on whether it is more likely than not that some portion of these deferred tax assets will not be realized. As of March 31, 2018, we concluded that it is more likely than not that a substantial portion of our deferred tax assets will be realized. As part of our analysis, we considered both positive and negative factors that impact profitability and whether those factors would lead to a change in the estimate of our deferred tax assets that may be realized in the future. Although the Tax Act may result in changes to our taxable income in the future, we do not anticipate that these changes would be significant enough to result in a change to our estimate when taken into account with other applicable factors. As of March 31, 2018, our conclusions on the valuation allowance and Internal Revenue Code Section 382 limitations related to our deferred tax assets remain consistent with the determinations we made during the period ended September 30, 2017, and such conclusions are based on similar company specific and industry factors to those discussed in Note 13 to the audited consolidated financial statements within our 2017 Annual Report.