Commitments and Contingencies - Letters of Credit (Details) - USD ($) $ in Millions	Dec. 31, 2017	Sep. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Outstanding letters of credit	$ 3.5	$ 3.5

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

No definition available.

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant