| Component: (Network and Table) | |
|---|---|
| Network | 40201 - Disclosure - Asset Retirement Obligations (Details) (http://www.natfuel.com/role/DisclosureAssetRetirementObligationsDetails) |
| Table | (Implied) |
| Reporting Entity [Axis] | 0000070145 (http://www.sec.gov/CIK) |
| Asset Retirement Obligations [Abstract] | Period [Axis] | ||
|---|---|---|---|
2012-10-01 - 2013-09-30 | 2011-10-01 - 2012-09-30 | 2010-10-01 - 2011-09-30 | |
Asset Retirement Obligations [Abstract] | |||
Balance at Beginning of Year | 119,246,000 | 75,731,000 | 101,618,000 |
Liabilities Incurred and Revisions of Estimates | (4,796,000) | 41,653,000 | 10,346,000 |
Liabilities Settled | (1,744,000) | (2,997,000) | (41,704,000) |
Accretion Expense | 6,805,000 | 4,859,000 | 5,471,000 |
Balance at End of Year | 119,511,000 | 119,246,000 | 75,731,000 |