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EMPLOYEE BENEFIT PLANS, REGULATORY ASSETS AND AOCI (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Sep. 30, 2015 | Sep. 30, 2014 | Sep. 30, 2013
Pension [Member] |  |  |
Amounts amortized to net periodic costs: |  |  |
Net actuarial (loss) gain | $ (6,985) | $ (5,596) | $ (7,646)
Prior service (cost) credit | (111) | (111) | (108)
Net transition obligation | 0 | 0 | 0
OPEB [Member] |  |  |
Amounts amortized to net periodic costs: |  |  |
Net actuarial (loss) gain | (2,943) | (2,500) | (3,857)
Prior service (cost) credit | 364 | 357 | 355
Net transition obligation | 0 | (11) | (26)
Regulatory Assets [Member] | Pension [Member] |  |  |
Regulatory Assets and Accumulated Other Comprehensive Income (Loss) |  |  |
Regulatory Assets, Balance at beginning of period | 61,794 | 56,664 |
Amounts arising during the period, Net actuarial loss (gain) | 30,579 | 10,563 |
Amounts amortized to net periodic costs: |  |  |
Net actuarial (loss) gain | (5,305) | (5,326) |
Prior service (cost) credit | (108) | (107) |
Net transition obligation | 0 | 0 |
Regulatory Assets, Balance at end of period | 86,960 | 61,794 | 56,664
Regulatory Assets [Member] | OPEB [Member] |  |  |
Regulatory Assets and Accumulated Other Comprehensive Income (Loss) |  |  |
Regulatory Assets, Balance at beginning of period | 43,774 | 41,812 |
Amounts arising during the period, Net actuarial loss (gain) | 9,563 | 4,277 |
Amounts amortized to net periodic costs: |  |  |
Net actuarial (loss) gain | (2,911) | (2,607) |
Prior service (cost) credit | 311 | 303 |
Net transition obligation | 0 | (11) |
Regulatory Assets, Balance at end of period | 50,737 | 43,774 | 41,812
Accumulated Other Comprehensive Income (Loss) [Member] | Pension [Member] |  |  |
Regulatory Assets and Accumulated Other Comprehensive Income (Loss) |  |  |
Accumulated Other Comprehensive Income (Loss), Balance at beginning of period | 17,581 | 14,427 |
Amounts arising during the period, Net actuarial loss (gain) | 9,742 | 6,243 |
Amounts amortized to net periodic costs: |  |  |
Net actuarial (loss) gain | (1,680) | (3,085) |
Prior service (cost) credit | (3) | (4) |
Net transition obligation | 0 | 0 |
Accumulated Other Comprehensive Income (Loss), Balance at end of period | 25,640 | 17,581 | 14,427
Accumulated Other Comprehensive Income (Loss) [Member] | OPEB [Member] |  |  |
Regulatory Assets and Accumulated Other Comprehensive Income (Loss) |  |  |
Accumulated Other Comprehensive Income (Loss), Balance at beginning of period | 117 | (2,142) |
Amounts arising during the period, Net actuarial loss (gain) | 1,103 | 2,098 |
Amounts amortized to net periodic costs: |  |  |
Net actuarial (loss) gain | (32) | 107 |
Prior service (cost) credit | 54 | 54 |
Net transition obligation | 0 | 0 |
Accumulated Other Comprehensive Income (Loss), Balance at end of period | $ 1,242 | $ 117 | $ (2,142)

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- Definition The pretax total of net gain (loss), prior service cost (credit), and transition assets (obligations), as well as minimum pension liability if still remaining, included in accumulated other comprehensive income associated with a defined benefit pension or other postretirement plan(s) because they have yet to be recognized as components of net periodic benefit cost. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (i-k) -URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669646-108580 + Details
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- Definition The amount of the prior service cost or credit recognized in net periodic benefit cost relating to benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(1) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Prior Service Cost -URI http://asc.fasb.org/extlink&oid=49177896 + Details
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- Definition Amount before tax of (increase) decrease in the value of the projected benefit obligation related to a change in an actuarial assumption and increase (decrease) in the value of the plan assets resulting from experience different from that assumed, that has not been recognized in net periodic benefit (cost) credit. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e637-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669646-108580 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 + Details
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