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EMPLOYEE BENEFIT PLANS - SUMMARY OF CHANGE IN FUNDED STATUS AND LIABILITIES (Details) - USD ($) $ in Thousands | 12 Months Ended
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Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2016
Postemployment employee (liability) |  |  |  |  |  |
Noncurrent |  | $ (137,007) |  | $ (128,888) |  |
Pension |  |  |  |  |  |
Change in Benefit Obligation |  |  |  |  |  |
Benefit obligation at beginning of year | [1] | 297,835 |  | 293,654 |  |
Service cost |  | 8,139 | [1] | 8,347 | [1] | $ 7,591
Interest cost |  | 10,493 | [1] | 9,771 | [1] | 11,342
Plan participants’ contributions | [1],[2] | 45 |  | 45 |  |
Special termination benefit |  | 3,730 | [1],[3] | 0 | [1],[3] | 0
Actuarial (gain) loss | [1] | (12,846) |  | (5,995) |  |
Benefits paid, net of retiree subsidies received | [1] | (8,821) |  | (7,987) |  |
Benefit obligation at end of year | [1] | 298,575 |  | 297,835 |  | 293,654
Change in plan assets |  |  |  |  |  |
Fair value of plan assets at beginning of year | [1] | 271,743 |  | 249,875 |  |
Actual return on plan assets | [1] | 16,306 |  | 29,736 |  |
Employer contributions | [1] | 137 |  | 74 |  |
Benefits paid, net of plan participants’ contributions | [1],[2] | (8,776) |  | (7,942) |  |
Fair value of plan assets at end of year | [1] | 279,410 |  | 271,743 |  | 249,875
Funded status | [1] | (19,165) |  | (26,092) |  |
Postemployment employee (liability) |  |  |  |  |  |
Current | [1] | (294) |  | (158) |  |
Noncurrent | [1] | (18,871) |  | (25,934) |  |
Total | [1] | (19,165) |  | (26,092) |  |
OPEB |  |  |  |  |  |
Change in Benefit Obligation |  |  |  |  |  |
Benefit obligation at beginning of year |  | 175,090 |  | 160,393 |  |
Service cost |  | 4,607 |  | 4,380 |  | 4,521
Interest cost |  | 6,365 |  | 5,545 |  | 6,256
Plan participants’ contributions | [2] | 161 |  | 120 |  |
Special termination benefit |  | 490 | [3] | 0 | [3] | 0
Actuarial (gain) loss |  | 15,145 |  | 8,985 |  |
Benefits paid, net of retiree subsidies received |  | (5,073) |  | (4,333) |  |
Benefit obligation at end of year |  | 196,785 |  | 175,090 |  | 160,393
Change in plan assets |  |  |  |  |  |
Fair value of plan assets at beginning of year |  | 71,534 |  | 62,035 |  |
Actual return on plan assets |  | 5,284 |  | 7,953 |  |
Employer contributions |  | 6,222 |  | 6,049 |  | 3,200
Benefits paid, net of plan participants’ contributions | [2] | (5,060) |  | (4,503) |  |
Fair value of plan assets at end of year |  | 77,980 |  | 71,534 |  | $ 62,035
Funded status |  | (118,805) |  | (103,556) |  |
Postemployment employee (liability) |  |  |  |  |  |
Current |  | (669) |  | (602) |  |
Noncurrent |  | (118,136) |  | (102,954) |  |
Total |  | $ (118,805) |  | $ (103,556) |  |
[1] | Includes the Company’s PEP.
[2] | Prior to July 1, 1998, employees were eligible to elect an additional participant contribution to enhance their benefits and contributions made during the periods were insignificant.
[3] | Related to the voluntary early retirement program offered during fiscal 2018, as previously discussed.

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