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