Pension Plan and Retirement Benefits - Defined Benefit Plans - Status (Details) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Defined Benefit Pension Plans
Change in Benefit Obligation:
Projected benefit obligation at beginning of year	$ 337,338	$ 311,943
Service cost	6,282	4,080	$ 3,898
Interest cost	10,577	12,050	11,203
Actuarial losses (gains)	(27,246)	32,370
Benefits paid	(14,682)	(23,105)
Administrative expenses	(1,466)
Projected benefit obligation at end of year	310,803	337,338	311,943
Change in Plan Assets:
Fair value of plan assets at beginning of year	207,963	205,498
Actual return on assets	25,475	18,792
Contribution to plan	6,804	6,778
Benefits paid	(14,682)	(23,105)
Administrative expenses	(1,466)
Fair value of plan assets at end of year	224,094	207,963	205,498
Funded Status of Plan:
Unfunded status	(86,709)	(129,375)
Postretirement Health Care Benefits
Change in Benefit Obligation:
Projected benefit obligation at beginning of year	125,117	110,534
Service cost	350	232	337
Interest cost	4,292	4,595	4,385
Actuarial losses (gains)	(8,072)	15,283
Benefits paid	(4,263)	(5,527)
Projected benefit obligation at end of year	117,424	125,117	$ 110,534
Change in Plan Assets:
Contribution to plan	4,263	5,527
Benefits paid	(4,263)	(5,527)
Funded Status of Plan:
Unfunded status	$ (117,424)	$ (125,117)

The difference between fair value of plan assets at the end of the period and the fair value at the beginning of the period, adjusted for contributions and payments of benefits during the period, and after adjusting for taxes and other expenses, as applicable.

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Amount of gain (loss) related to change in benefit obligation resulting from changes in actuarial assumptions, for example, but not limited to, interest, mortality, employee turnover, salary, and temporary deviation from the substantive plan.

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Amount of plan administration expenses deducted from total plan assets.

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1) For defined benefit pension plans, the benefit obligation is the projected benefit obligation, which is the actuarial present value as of a date of all benefits attributed by the pension benefit formula to employee service rendered prior to that date. 2) For other postretirement defined benefit plans, the benefit obligation is the accumulated postretirement benefit obligation, which is the actuarial present value of benefits attributed to employee service rendered to a particular date.

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The amount of payments made for which participants are entitled under a pension plan, including pension benefits, death benefits, and benefits due on termination of employment. Also includes payments made under a postretirement benefit plan, including prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services. This item represents a periodic decrease to the plan obligations and a decrease to plan assets.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of contributions made by the employer to defined benefit plans.

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Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees.

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The funded status is measured as the difference between the fair value of plan assets and the benefit obligation. Will normally be the same as the net Defined Benefit Plan, Amounts Recognized in Balance Sheet, Total.

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The increase in a defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation due to the passage of time.

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The actuarial present value of benefits attributed by the pension benefit formula to services rendered by employees during the period. The portion of the expected postretirement benefit obligation attributed to employee service during the period. The service cost component is a portion of the benefit obligation and is unaffected by the funded status of the plan.

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