Summary of Significant Accounting - Future Undiscounted Losses (Details) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2018	Sep. 30, 2017
Summary Of Significant Accounting Policies [Abstract]
EstimatedUndiscountedUltimateLossesInNextTwelveMonths	$ 1,748
EstimatedUndiscountedUltimateLossesInYearTwo	1,144
EstimatedUndiscountedUltimateLossesInYearThree	746
EstimatedUndiscountedUltimateLossesInYearFour	429
EstimatedUndiscountedUltimateLossesInYearFive	216
EstimatedUndiscountedUltimateLossesThereafter	1,003
Loss Contingency, Undiscounted Amount of Insurance-related Assessment Liability	$ 5,286	$ 5,306

The liability as of the balance sheet date representing required funding mandated by statute or regulatory authority that is related directly or indirectly to underwriting activities, including pools for self-insurance and excluding premium taxes and income taxes. The funds derived from the assessments generally enable a government guarantor to pay insurance claims in the event that the underwriting insurer is insolvent or otherwise unable to meet its payment obligations.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 405
-SubTopic 30
-Section 15
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=51828112&loc=d3e23169-109297

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 405
-SubTopic 30
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6392405&loc=d3e24119-109301

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration