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EMPLOYEE BENEFIT PLANS - Fair Value (Details) - USD ($) $ in Thousands | Sep. 30, 2016 | Sep. 30, 2015 | Sep. 30, 2014
--- | --- | --- | ---
PLAN ASSETS |  |  |
Fair value of plan assets | $ 90,748 | $ 98,060 | $ 108,157
Oil and Gas Properties |  |  |
PLAN ASSETS |  |  |
Fair value of plan assets | 177 | 387 | $ 301
Quoted Prices in Active Markets for Identical Assets (Level 1) |  |  |
PLAN ASSETS |  |  |
Fair value of plan assets | 90,571 | 97,673 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term investments. |  |  |
PLAN ASSETS |  |  |
Fair value of plan assets | 467 | 2,248 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Mutual funds |  |  |
PLAN ASSETS |  |  |
Fair value of plan assets | 70,250 | 78,060 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Domestic stock funds |  |  |
PLAN ASSETS |  |  |
Fair value of plan assets | 36,107 | 40,072 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Bond funds |  |  |
PLAN ASSETS |  |  |
Fair value of plan assets | 22,809 | 25,344 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | International stock funds |  |  |
PLAN ASSETS |  |  |
Fair value of plan assets | 11,334 | 12,644 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Domestic common stock |  |  |
PLAN ASSETS |  |  |
Fair value of plan assets | 18,305 | 15,883 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Foreign equity stock |  |  |
PLAN ASSETS |  |  |
Fair value of plan assets | 1,549 | 1,482 |
Significant Unobservable Inputs (Level 3) |  |  |
PLAN ASSETS |  |  |
Fair value of plan assets | 177 | 387 |
Significant Unobservable Inputs (Level 3) | Oil and Gas Properties |  |  |
PLAN ASSETS |  |  |
Fair value of plan assets | 177 | 387 |
Total Measure at Fair Value |  |  |
PLAN ASSETS |  |  |
Fair value of plan assets | 90,748 | 98,060 |
Total Measure at Fair Value | Short-term investments. |  |  |
PLAN ASSETS |  |  |
Fair value of plan assets | 467 | 2,248 |
Total Measure at Fair Value | Mutual funds |  |  |
PLAN ASSETS |  |  |
Fair value of plan assets | 70,250 | 78,060 |
Total Measure at Fair Value | Domestic stock funds |  |  |
PLAN ASSETS |  |  |
Fair value of plan assets | 36,107 | 40,072 |
Total Measure at Fair Value | Bond funds |  |  |
PLAN ASSETS |  |  |
Fair value of plan assets | 22,809 | 25,344 |
Total Measure at Fair Value | International stock funds |  |  |
PLAN ASSETS |  |  |
Fair value of plan assets | 11,334 | 12,644 |
Total Measure at Fair Value | Domestic common stock |  |  |
PLAN ASSETS |  |  |
Fair value of plan assets | 18,305 | 15,883 |
Total Measure at Fair Value | Foreign equity stock |  |  |
PLAN ASSETS |  |  |
Fair value of plan assets | 1,549 | 1,482 |
Total Measure at Fair Value | Oil and Gas Properties |  |  |
PLAN ASSETS |  |  |
Fair value of plan assets | $ 177 | $ 387 |

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