Basis of Presentation and Significant Accounting Policies - Concentrations of Credit Risk (Details)	3 Months Ended	12 Months Ended
Dec. 31, 2018	Sep. 30, 2018
Cash and Cash Equivalents and Restricted Cash \| US Treasuries and FDIC Insured
Concentration Risk [Line Items]
Concentration risk, percentage	62.00%	65.00%
Customer One \| Accounts Receivable \| Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	16.00%	23.00%

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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6404-108592

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