Accounting Changes and Recent Accounting Pronouncements (Policies)	12 Months Ended
Sep. 30, 2020
New Accounting Pronouncements And Changes In Accounting Principles [Abstract]
Accounting Changes	Accounting Changes In February 2016, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2016-02 which requires most leases to be reported on the balance sheet as a right-of-use asset and a lease liability. On October 1, 2019, we adopted ASU No. 2016-02 using a modified retrospective transition method without restating comparative periods. We have elected the package of practical expedients permitted within the transition guidance under the new standard relating to the identification, classification and initial direct costs of leases commencing before the effective date of Topic 842. In addition, we have elected to not recognize a right-of-use asset or lease obligation for short-term leases with an initial term of 12 months or less. The adoption of ASU No. 2016-02, as amended, resulted in the recognition of an operating lease asset of $513.9 million and an operating lease liability of $523.5 million. Existing straight-line rent liability, prepaid rent and accrued rent were reclassified from certain other assets and liabilities into the operating lease asset. Furthermore, the cumulative effect of the adoption of ASU No. 2016-02 resulted in a $0.1 million adjustment to accumulated earnings resulting from the impairment of certain operating lease assets as well certain deferred tax balances that were written off as a result of the adoption of the new standard. The impact on our consolidated results of operations or consolidated cash flows was not material. See Note 8 for additional information in connection with ASU No. 2016-02. Effective August 1, 2020, we changed our method of accounting for inventory located in the U.S. and Canada at both our distribution centers and store fronts. Prior to August 2020, we valued inventory at the lower of cost or net realizable value on a FIFO basis. Effective August 1, 2020, all company-wide inventories have been valued at the lower of cost or net realizable value using the weighted average cost method. These changes were made in connection with the implementation of a new perpetual inventory system, which provides us with better information to manage inventory. We believe the weighted average cost method is preferable to the FIFO cost method because it results in greater precision in the determination of cost of goods sold and inventories at the SKU level and results in a consistent inventory valuation method for all of the Company’s inventories. We recorded the cumulative effect of this change in accounting principle as of August 1, 2020. The effects of this change in accounting principle as of August 1, 2020 were not material to our consolidated financial statements. Prior to implementation of the new perpetual inventory system, we were not able to determine the impact of the change to the weighted average cost method. Therefore, we did not retroactively apply the change to prior periods.
Recent Accounting Pronouncements	In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (“ASC 740”), which simplifies the accounting for income taxes by removing an exception related to the approach for intraperiod tax allocation, the methodology for calculating income taxes in an interim period with year to date losses and the recognition of deferred tax liabilities for outside basis differences. Additionally, the update clarifies and simplifies other areas of ASC 740, Income Taxes. For public companies, the amendments in the update are effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020. Early adoption is permitted, but all amendments must be adopted at once. The amendments in this update have different adoption methods including prospective basis, retrospective basis, and a modified retrospective basis dependent on the specific change. We are currently evaluating the impact of this update.

Accounting Changes and Recent Accounting Pronouncements (Policies)

12 Months Ended

Sep. 30, 2020

New Accounting Pronouncements And Changes In Accounting Principles [Abstract]

In February 2016, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2016-02 which requires most leases to be reported on the balance sheet as a right-of-use asset and a lease liability. On October 1, 2019, we adopted ASU No. 2016-02 using a modified retrospective transition method without restating comparative periods. We have elected the package of practical expedients permitted within the transition guidance under the new standard relating to the identification, classification and initial direct costs of leases commencing before the effective date of Topic 842. In addition, we have elected to not recognize a right-of-use asset or lease obligation for short-term leases with an initial term of 12 months or less. The adoption of ASU No. 2016-02, as amended, resulted in the recognition of an operating lease asset of $513.9 million and an operating lease liability of $523.5 million. Existing straight-line rent liability, prepaid rent and accrued rent were reclassified from certain other assets and liabilities into the operating lease asset. Furthermore, the cumulative effect of the adoption of ASU No. 2016-02 resulted in a $0.1 million adjustment to accumulated earnings resulting from the impairment of certain operating lease assets as well certain deferred tax balances that were written off as a result of the adoption of the new standard. The impact on our consolidated results of operations or consolidated cash flows was not material. See Note 8 for additional information in connection with ASU No. 2016-02.

Effective August 1, 2020, we changed our method of accounting for inventory located in the U.S. and Canada at both our distribution centers and store fronts. Prior to August 2020, we valued inventory at the lower of cost or net realizable value on a FIFO basis. Effective August 1, 2020, all company-wide inventories have been valued at the lower of cost or net realizable value using the weighted average cost method. These changes were made in connection with the implementation of a new perpetual inventory system, which provides us with better information to manage inventory. We believe the weighted average cost method is preferable to the FIFO cost method because it results in greater precision in the determination of cost of goods sold and inventories at the SKU level and results in a consistent inventory valuation method for all of the Company’s inventories. We recorded the cumulative effect of this change in accounting principle as of August 1, 2020. The effects of this change in accounting principle as of August 1, 2020 were not material to our consolidated financial statements. Prior to implementation of the new perpetual inventory system, we were not able to determine the impact of the change to the weighted average cost method. Therefore, we did not retroactively apply the change to prior periods.

Recent Accounting Pronouncements

In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (“ASC 740”), which simplifies the accounting for income taxes by removing an exception related to the approach for intraperiod tax allocation, the methodology for calculating income taxes in an interim period with year to date losses and the recognition of deferred tax liabilities for outside basis differences. Additionally, the update clarifies and simplifies other areas of ASC 740, Income Taxes. For public companies, the amendments in the update are effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020. Early adoption is permitted, but all amendments must be adopted at once. The amendments in this update have different adoption methods including

prospective basis, retrospective basis, and a modified retrospective basis dependent on the specific change. We are currently evaluating the impact of this update.