The revenue of off system sales attributable to the entity.

No definition available.

Name:	lg_CompanyShare
Namespace Prefix:	lg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of savings due to cost management program allowed to be retained by the entity.

+ References

No definition available.

+ Details

Name:	lg_CostSavingsRetentionPercentage
Namespace Prefix:	lg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The revenue of off system sales attributable to customers.

+ References

No definition available.

+ Details

Name:	lg_CustomerShare
Namespace Prefix:	lg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of gross receipts taxes associated with natural gas utility service, which are imposed on the Utility and billed to its customers.

+ References

No definition available.

+ Details

Name:	lg_GrossReceiptsTaxAmountsIncludedOperatingRevenues
Namespace Prefix:	lg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Maximum amount of annual cost savings that the utility is able to retain under cost savings plan.

+ References

No definition available.

+ Details

Name:	lg_MaximumAmountOfCostSavingsAllowable
Namespace Prefix:	lg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Minimum number of months that is required between discretionary PGA changes.

+ References

No definition available.

+ Details

Name:	lg_MonthsbetweenPGADiscretionaryChanges
Namespace Prefix:	lg_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of months the original maturity of debt instruments purchased can not exceed to be considered cash equivalents.

+ References

No definition available.

+ Details

Name:	lg_NumberofMonthsoftheOriginalMaturityofDebtInstrumentsPurchased
Namespace Prefix:	lg_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of discretionary PGA changes the Utility can make during each fiscal year.

+ References

No definition available.

+ Details

Name:	lg_NumberofPGADiscretionaryChanges
Namespace Prefix:	lg_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	lg_OffSystemSalesLineItems
Namespace Prefix:	lg_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Part 4 (Details) (USD $)	12 Months Ended
	Sep. 30, 2013 change	Sep. 30, 2012	Sep. 30, 2011
Off System Sales [Line Items]
Number of PGA Discretionary Changes	3
Months between PGA Discretionary Changes	2 months
Cost savings retention percentage	10.00%
Maximum amount of cost savings allowable	$ 3,000,000.0
Number of Months of the Original Maturity of Debt Instruments Purchased	3 months
Gross Receipts taxes recorded in regulated gas distribution operating revenues	$ 40,800,000	$ 35,900,000	$ 43,500,000
Laclede Gas [Member] \| First $2 million [Member]
Off System Sales [Line Items]
Customer Share	100.00%
Company Share	0.00%
Laclede Gas [Member] \| Next $2 million [Member]
Off System Sales [Line Items]
Customer Share	80.00%
Company Share	20.00%
Laclede Gas [Member] \| Next $2 million [Member]
Off System Sales [Line Items]
Customer Share	75.00%
Company Share	25.00%
Laclede Gas [Member] \| Amounts exceeding $6 million [Member]
Off System Sales [Line Items]
Customer Share	70.00%
Company Share	30.00%
Missouri Gas Energy (MGE) [Member] \| First $1.2 million [Member]
Off System Sales [Line Items]
Customer Share	85.00%
Company Share	15.00%
Missouri Gas Energy (MGE) [Member] \| Next $1.2 million [Member]
Off System Sales [Line Items]
Customer Share	80.00%
Company Share	20.00%
Missouri Gas Energy (MGE) [Member] \| Next $1.2 million [Member]
Off System Sales [Line Items]
Customer Share	75.00%
Company Share	25.00%
Missouri Gas Energy (MGE) [Member] \| Amounts exceeding $3.6 million [Member]
Off System Sales [Line Items]
Customer Share	70.00%
Company Share	30.00%