Fair Value Measurements - Additional Information (Details) - USD ($)	Mar. 31, 2019	Sep. 30, 2018	Mar. 31, 2018
Spire Alabama
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Outstanding derivative contracts	$ 0	$ 0	$ 0

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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