Regulatory Matters - Spire - Additional Information (Details) - USD ($) $ in Thousands			1 Months Ended	12 Months Ended
	Sep. 14, 2018	Feb. 01, 2018	Dec. 31, 2015	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Public Utilities, General Disclosures [Line Items]
Regulatory costs				$ 0	$ 30,600	$ 0
Spire Gulf
Public Utilities, General Disclosures [Line Items]
Approved return rate on equity				10.70%
Rate increase (decrease), margin of index range				1.50%
Pro-rate rating for equity content				75.00%
Revenue variances				$ 100
Single force majeure				100
Multiple force majeures				$ 150
Recovery percentage of incurred costs				90.00%
Approved point to refund				$ 900
Approved rate increase (decrease) amount				$ 1,500
Spire
Public Utilities, General Disclosures [Line Items]
Regulatory costs		$ 1,900
Spire Mississippi
Public Utilities, General Disclosures [Line Items]
Approved return rate on equity				10.36%
Excess of allowed return on equity				1.00%
Return on equity shortfall				75.00%
Excess return on equity				50.00%
Recovery period			3 years
APSC | Spire
Public Utilities, General Disclosures [Line Items]
Line of credit facility borrowing capacity				$ 50,000
Principal amount outstanding				$ 25,000
MoPSC
Public Utilities, General Disclosures [Line Items]
Approved rate increase (decrease), annualized revenue	$ 700
Minimum [Member] | Spire Gulf
Public Utilities, General Disclosures [Line Items]
Approved return rate on equity				10.45%
Maximum | Spire Gulf
Public Utilities, General Disclosures [Line Items]
Approved return rate on equity				10.95%