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Retirement Benefits (Schedule of Allocation of Plan Assets, Fair Value Hierarchy) (Details) - USD ($) $ in Thousands | Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2017
--- | --- | --- | ---
Defined Benefit Pension Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | $ 234,133 | $ 227,722 | $ 224,712
Defined Benefit Pension Plan [Member] | Cash and Cash Equivalents [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 2,986 | 3,225 |
Defined Benefit Pension Plan [Member] | Pooled funds: Index linked U.K. government securities fund [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 5,491 | 4,913 |
Defined Benefit Pension Plan [Member] | Pooled funds: Index linked U.K. long-term government securities fund [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 7,898 | 6,817 |
Defined Benefit Pension Plan [Member] | Mutual funds: U.S. corporate bond fund [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 64,514 | 54,699 |
Defined Benefit Pension Plan [Member] | Pooled funds: Index linked U.K. corporate bonds fund [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 16,737 | 16,121 |
Defined Benefit Pension Plan [Member] | Mutual funds: U.S. equity large cap fund [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 56,829 | 60,176 |
Defined Benefit Pension Plan [Member] | Mutual funds: International equity large cap growth fund [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 46,645 | 47,559 |
Defined Benefit Pension Plan [Member] | Pooled funds: Japanese equity securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 2,518 | 2,506 |
Defined Benefit Pension Plan [Member] | Pooled funds: International equity securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 2,226 | 2,214 |
Defined Benefit Pension Plan [Member] | Pooled funds: Index linked U.K. equity fund [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 3,738 | 4,326 |
Defined Benefit Pension Plan [Member] | Pooled funds: Index linked international equity fund [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 5,438 | 5,973 |
Defined Benefit Pension Plan [Member] | Pooled funds: Japanese fixed income securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 4,915 | 4,968 |
Defined Benefit Pension Plan [Member] | Pooled funds: International fixed income securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 1,710 | 1,730 |
Defined Benefit Pension Plan [Member] | Global Target Return Equity/Bond Fund [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 12,488 | 12,495 |
Other Postretirement Benefit Plans [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets |  |  |
United States [Member] | Defined Benefit Pension Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 170,556 | 165,342 | 160,332
United States [Member] | Defined Benefit Pension Plan [Member] | Fair Value Hierarchy Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 170,556 | 165,342 |
United States [Member] | Defined Benefit Pension Plan [Member] | Fair Value Hierarchy Level 1 [Member] | Cash and Cash Equivalents [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 2,568 | 2,908 |
United States [Member] | Defined Benefit Pension Plan [Member] | Fair Value Hierarchy Level 1 [Member] | Mutual funds: U.S. corporate bond fund [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 64,514 | 54,699 |
United States [Member] | Defined Benefit Pension Plan [Member] | Fair Value Hierarchy Level 1 [Member] | Mutual funds: U.S. equity large cap fund [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 56,829 | 60,176 |
United States [Member] | Defined Benefit Pension Plan [Member] | Fair Value Hierarchy Level 1 [Member] | Mutual funds: International equity large cap growth fund [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 46,645 | 47,559 |
Other Countries [Member] | Defined Benefit Pension Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 63,577 | 62,380 | $ 64,380
Other Countries [Member] | Defined Benefit Pension Plan [Member] | Fair Value Hierarchy Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 418 | 317 |
Other Countries [Member] | Defined Benefit Pension Plan [Member] | Fair Value Hierarchy Level 1 [Member] | Cash and Cash Equivalents [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 418 | 317 |
Other Countries [Member] | Defined Benefit Pension Plan [Member] | Fair Value Hierarchy Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 63,159 | 62,063 |
Other Countries [Member] | Defined Benefit Pension Plan [Member] | Fair Value Hierarchy Level 2 [Member] | Pooled funds: Index linked U.K. government securities fund [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 5,491 | 4,913 |
Other Countries [Member] | Defined Benefit Pension Plan [Member] | Fair Value Hierarchy Level 2 [Member] | Pooled funds: Index linked U.K. long-term government securities fund [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 7,898 | 6,817 |
Other Countries [Member] | Defined Benefit Pension Plan [Member] | Fair Value Hierarchy Level 2 [Member] | Pooled funds: Index linked U.K. corporate bonds fund [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 16,737 | 16,121 |
Other Countries [Member] | Defined Benefit Pension Plan [Member] | Fair Value Hierarchy Level 2 [Member] | Pooled funds: Japanese equity securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 2,518 | 2,506 |
Other Countries [Member] | Defined Benefit Pension Plan [Member] | Fair Value Hierarchy Level 2 [Member] | Pooled funds: International equity securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 2,226 | 2,214 |
Other Countries [Member] | Defined Benefit Pension Plan [Member] | Fair Value Hierarchy Level 2 [Member] | Pooled funds: Index linked U.K. equity fund [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 3,738 | 4,326 |
Other Countries [Member] | Defined Benefit Pension Plan [Member] | Fair Value Hierarchy Level 2 [Member] | Pooled funds: Index linked international equity fund [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 5,438 | 5,973 |
Other Countries [Member] | Defined Benefit Pension Plan [Member] | Fair Value Hierarchy Level 2 [Member] | Pooled funds: Japanese fixed income securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 4,915 | 4,968 |
Other Countries [Member] | Defined Benefit Pension Plan [Member] | Fair Value Hierarchy Level 2 [Member] | Pooled funds: International fixed income securities [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 1,710 | 1,730 |
Other Countries [Member] | Defined Benefit Pension Plan [Member] | Fair Value Hierarchy Level 2 [Member] | Global Target Return Equity/Bond Fund [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 12,488 | $ 12,495 |
Japan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 11,472 |  |
United Kingdom |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | $ 52,105 |  |

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