Stock-Based Awards - Data Used to Determine Value of Stock Option Grants, Presented on Weighted Average Basis (Detail)	12 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Share Based Payment Award Stock Options Valuation Assumptions [Line Items]
Expected volatility	55.00%	57.00%	60.00%
Risk-free interest rate	2.76%	2.29%	1.97%
Expected term (in years)	6 years 18 days	6 years 18 days	6 years 18 days
Expected dividends	0.00%	0.00%	0.00%
Executive Officer [Member] \| Relative Total Stockholder Return Units [Member]
Share Based Payment Award Stock Options Valuation Assumptions [Line Items]
Expected volatility	62.00%	62.00%	66.00%
Expected term (in years)	2 years 10 days	1 year 9 months 29 days	1 year 11 months 26 days
Risk-free interest rate	2.65%	2.18%	1.24%
Expected dividends	0.00%	0.00%	0.00%

The expected dividend rate assumption that is used in valuing a relative total stockholder return unit.

No definition available.

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- Definition

The risk-free interest rate assumption that is used in valuing a relative total stockholder return unit.

+ References

No definition available.

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- Definition

Share based payment award stock options valuation assumptions.

+ References

No definition available.

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- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

+ References

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- Definition

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

+ References

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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

+ References

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- Definition

Expected term of award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(i)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.D.2)
-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

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