Summary of Significant Accounting Policies - Concentration of Credit Risk (Details)	12 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Top Ten Largest Customers \| Credit Concentration Risk \| Revenue from Contract with Customer, Product and Service Benchmark
Concentration Risk [Line Items]
Concentration risk, percentage (as a percent)	33.00%	28.00%	34.00%

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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