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Note 15 - Regulatory Matters (Details Textual) - USD ($) $ in Thousands |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 Months Ended | 3 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Dec. 01, 2023 | Oct. 04, 2023 | Sep. 01, 2023 | Apr. 30, 2023 | Apr. 20, 2023 | Jan. 01, 2023 | Nov. 18, 2022 | Apr. 22, 2022 | Feb. 01, 2022 | Jan. 01, 2022 | Dec. 29, 2021 | Dec. 23, 2021 | Oct. 26, 2021 | Oct. 01, 2018 | Sep. 30, 2022 | Feb. 28, 2021 | Nov. 30, 2019 | Mar. 31, 2022 | Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2021 | Jan. 25, 2023
Customer Share |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 75.00% |  |  |
Utilities Operating Expense, Gas and Petroleum Purchased |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,260,800 | $ 923,900 | $ 946,300 |
Missouri Public Service Commission [Member] | Infrastructure System Replacement Surcharge [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amount |  |  |  |  |  |  |  |  |  |  |  | $ 47,300 |  |  |  |  |  |  |  |  |  |  |
Alabama Public Service Commission [Member] | Enhanced Stability Reserve [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Utilities Operating Expense Maintenance and Operations Self Insurance Cost Deferred Amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,000 |  |
Utilities Operating Expense Maintenance and Operations Self Insurance Cost Single Force Majeure Event Deferred Amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 300 |  |  |
Utilities Operating Expense Maintenance and Operations Self Insurance Cost Multiple Force Majeure Events Deferred Amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 400 |  |  |
Regulated Operating Revenue Variances Amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 400 |  |  |
Regulated Operations Enhanced Stability Reserve Underfunded Balances Amortization Term (Year) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5 years |  |  |
Regulated Operations, Enhanced Stability Reserve, Unfunded Balances, Amortization, Annual Limitation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 700 |  |  |
Spire Missouri [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Customer Share |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 25.00% |  |  |
Utilities Operating Expense, Gas and Petroleum Purchased |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 195,800 |  |  |  | $ 943,400 | 587,000 | 786,800 |
Public Utilities, Reduced Revenue Accounts Receivable Cost Of Gas and Regulatory Liabilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 150,000 |  |  |  |  |
Utilities Operating, Due From Other Parties |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 42,000 |  |  |  |  |
Spire Missouri [Member] | Missouri Public Service Commission [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Approved Rate Increase (Decrease), Amount |  |  |  |  |  |  | $ 78,000 |  |  |  |  | 72,200 |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amount |  |  |  |  |  |  |  |  |  |  |  | $ 24,900 |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Deferred Amount Under Order Authorizing Accounting Treatment |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 42,800 |  |  |  |  |  | 42,800 |  |
Public Utilities, Approved Rate, Increase Decrease Annualized Revenue |  |  |  |  | $ 7,700 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Disallowance From ACA Balance |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 600
Spire Missouri [Member] | Missouri Public Service Commission [Member] | Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Approved Rate, Increase Decrease Annualized Revenue |  | $ 12,400 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Spire Missouri [Member] | Missouri Public Service Commission [Member] | Infrastructure System Replacement Surcharge [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Approved Rate Increase (Decrease), Amount |  |  |  |  |  |  | $ 19,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Spire Alabama Inc [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Utilities Operating Expense, Gas and Petroleum Purchased |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 202,700 | $ 161,500 | 145,300 |
Public Utilities, Rate Increase Decrease Index Range Margin |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1.50% |  |  |  |  |  | 1.50% |  |
Public Utilities, Approved Point of Test Giveback Under Rate Stabilization and Equalization |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 2,200 |  |  |  |  |  | $ 2,200 | 2,200 |
Financing Receivable, after Allowance for Credit Loss |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 7,100 |  |  |  |  | 6,700 | 7,100 |  |
Spire Alabama Inc [Member] | Maximum [Member] | Spire [Member] | Related Party [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Financing Receivable, after Allowance for Credit Loss |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 25,000 |  |  |
Spire Alabama Inc [Member] | Alabama Public Service Commission [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Approved Rate Increase (Decrease), Amount |  |  |  |  |  |  |  |  |  | $ 5,300 |  |  |  |  |  |  |  |  |  | 4,400 |  | 8,800 |
Public Utilities, Requested Rate Increase (Decrease), Amount |  |  |  |  |  |  |  |  |  |  | $ 5,300 |  |  |  |  |  |  |  |  |  | $ 17,200 |  |
Public Utilities Maximum Return on Equity Percentage of Prior Year Revenues |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4.00% |  |  |  |  |  | 4.00% |  |
Public Utilities, Approved Return on Equity, Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  | 10.40% | 9.70% |  |  |  |  |  |  |  |
Public Utilities, Rate Increase Decrease Index Range Margin |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.10% |  |  |  |  |  | 0.10% |  |
Public Utilities, Equity Limitation as Percent of Total Capitalization |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 55.50% |  |  |  |  |  | 55.50% |  |
Public Utilities, Equity Limitation as Percent of Average Common Equity Growth |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6.00% |  |  |  |  |  | 6.00% |  |
Annual Revenue Increase From Rates, Amount |  |  |  |  |  | $ 15,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities Approved Percentage of Excess Natural Gas Supply and Capacity to Customers |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 75.00% |  |  |  |  |  |
Public Utilities Approved Percentage of Excess Natural Gas Supply and Capacity To Retain |  |  |  |  |  |  |  | 25.00% |  |  |  |  |  |  |  |  | 25.00% |  |  |  |  |  |
Public Utilities, Value From Capacity Release, Threshold |  |  |  |  |  |  |  | $ 1,600 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Spire Alabama Inc [Member] | Alabama Public Service Commission [Member] | Forecast [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual Revenue Increase From Rates, Amount | $ 15,800 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Spire Alabama Inc [Member] | Alabama Public Service Commission [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Approved Return on Equity, Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  | 10.15% | 9.50% |  |  |  |  |  |  |  |
Spire Alabama Inc [Member] | Alabama Public Service Commission [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Approved Return on Equity, Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  | 10.65% | 9.90% |  |  |  |  |  |  |  |
Spire Gulf [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Approved Rate Increase (Decrease), Amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,700 | 2,300 |
Public Utilities, Approved Rate, Increase Decrease Annualized Revenue |  |  |  | $ 1,800 |  | 2,500 |  |  |  | $ 1,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Approved Return on Equity, Percentage |  |  |  |  |  |  |  |  |  |  |  |  | 9.95% |  |  |  |  |  |  |  | 10.70% |  |
Public Utilities, Rate Increase Decrease Index Range Margin |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1.50% |  |  |  |  |  | 1.50% |  |
Utilities Operating Expense Maintenance and Operations Self Insurance Cost Single Force Majeure Event Deferred Amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 100 |  |  |
Utilities Operating Expense Maintenance and Operations Self Insurance Cost Multiple Force Majeure Events Deferred Amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 150 |  |  |
Regulated Operating Revenue Variances Amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 100 |  |  |
Public Utilities, Approved Rate, Net Income Benefit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,600 |
Public Utilities, Approved Return on Equity, Pro-Rata, Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 75.00% |  |  |
Regulated Operations, Recovery of Incurred Costs, Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 90.00% |  |  |
Spire Gulf [Member] | Forecast [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Approved Rate, Increase Decrease Annualized Revenue | $ 2,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Approved Return on Equity, Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 9.95% |  |  |  |
Spire Gulf [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Approved Return on Equity, Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10.45% |  |
Spire Gulf [Member] | Minimum [Member] | Forecast [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Approved Return on Equity, Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 9.70% |  |  |  |
Spire Gulf [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Approved Return on Equity, Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10.95% |  |
Spire Gulf [Member] | Maximum [Member] | Forecast [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Approved Return on Equity, Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10.30% |  |  |  |
Spire [Member] | Alabama Public Service Commission [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility, Maximum Borrowing Capacity |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 75,000 |  |  |
Spire Mississippi [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Approved Rate Increase (Decrease), Amount |  |  | $ 1,300 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Approved Rate, Increase Decrease Annualized Revenue |  |  |  |  |  | $ 800 |  |  | $ 800 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Approved Return on Equity, Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10.04% |  |  |
Public Utilities, Approved Return on Equity, Excess of Allowed Return, Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1.00% |  |  |
Public Utilities, Approved Return on Equity Shortfall Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 75.00% |  |  |
Public Utilities, Approved Return On Equity, Excess, Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 50.00% |  |  |
Future Income Taxes Due From Customers and Pension and Other Postretirement Benefit Costs [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Remaining Recovery Period of Regulatory Assets for which No Return on Investment During Recovery Period is Provided (Year) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 20 years |  |  |
PGA Assets [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Remaining Recovery Period of Regulatory Assets for which No Return on Investment During Recovery Period is Provided (Year) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 years |  |  |
PGA Assets Not Earning A Return [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Remaining Recovery Period of Regulatory Assets for which No Return on Investment During Recovery Period is Provided (Year) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 15 years |  |  |

X
- Definition The amount of annual revenue increase from new rates. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition The revenue of off system sales attributable to customers. + References No definition available. + Details
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- Definition Approved percentage of excess natural gas supply and capacity to customers under public utilities. + References No definition available. + Details
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- Definition Approved percentage of excess natural gas supply and capacity to retain for public utilities. + References No definition available. + Details
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- Definition Amounts of approved point of test giveback under rate stabilization and equalization for public utilities. + References No definition available. + Details
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- Definition Public Utilities, Approved Rate Increase (Decrease), Annualized Revenue + References No definition available. + Details
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- Definition Represents approved rate of net income benefit under public utilities. + References No definition available. + Details
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- Definition Percentage of excess of allowed return of approved return on equity of public utilities. + References No definition available. + Details
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Data Type: | dtr-types:percentItemType
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- Definition Percentage of excess of approved return on equity for public utilities. + References No definition available. + Details
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- Definition Pro-rata percentage of approved return on equity under public utilities. + References No definition available. + Details
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- Definition Percentage of shortfall for approved return on equity of public utilities. + References No definition available. + Details
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Data Type: | dtr-types:percentItemType
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- Definition Public utilities deferred amount under order authorizing accounting treatment. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition The amount of public utilities disallowance from ACA balance. + References No definition available. + Details
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Namespace Prefix: | sr_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Represents the equity limitation as a percentage of average common equity growth. + References No definition available. + Details
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Data Type: | dtr-types:percentItemType
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- Definition Represents equity limitation as a percentage of total capitalization by regulatory agency. + References No definition available. + Details
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Data Type: | dtr-types:percentItemType
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- Definition Percentage of prior year revenues for maximum return on equity under public utilities. + References No definition available. + Details
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- Definition Represents rate increase decrease index range margin for public utilities. + References No definition available. + Details
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Balance Type: | na
Period Type: | instant

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- Definition Public utilities reduced revenue, accounts receivable, cost of gas and regulatory liabilities. + References No definition available. + Details
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Namespace Prefix: | sr_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Represents the threshold value from capacity release with regulatory agency. + References No definition available. + Details
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Namespace Prefix: | sr_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Variance amount of revenue for regulated operating. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Amortization term of underfunded balances of enhanced stability reserve under regulated operations. + References No definition available. + Details
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- Definition Amount of annual limitation of amortization of unfunded balances for enhanced stability reserve under regulated operations. + References No definition available. + Details
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Balance Type: | credit
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- Definition Percentage of recovery of incurred costs under regulated operations. + References No definition available. + Details
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Data Type: | dtr-types:percentItemType
Balance Type: | na
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- Definition Amount of receivables from other parties. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Amounts of maintenance and operations and self insurance cost for utilities operating expense. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Amount of maintenance and operations self insurance cost of multiple force majeure events as utilities operating expense. + References No definition available. + Details
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