Stock-Based Compensation - Employee Stock Purchase Plan (Details) - shares	3 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued under employee stock purchase plan (in shares)	0	0
Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Purchase price of common stock (as a percent)	85.00%

Number of shares issued during the period as a result of an employee stock purchase plan.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Name:	us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration