Other Comprehensive Income (Loss) (Schedule of Items Reclassified out of AOCL) (Details) - USD ($)	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amount reclassified	$ (71,600,000)	$ (42,600,000)
Tax effect	12,800,000	2,800,000
Net of tax	(58,800,000)	(39,800,000)
Net activity	36,900,000	21,200,000
Stockholders' Equity Attributable to Parent	1,763,100,000		$ 1,726,100,000
Available-for-sale Securities and Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	(3,400,000)	900,000
Net of tax	(2,600,000)	600,000
Prior to reclassification	(3,000,000.0)	(4,200,000)
Other Comprehensive Income (Loss), before Tax	(6,400,000)	(3,300,000)
Other Comprehensive Income (Loss), Tax	(1,500,000)	(700,000)
Net activity	(4,900,000)	(2,600,000)
Stockholders' Equity Attributable to Parent	(34,200,000)	4,600,000	(29,300,000)	$ 7,200,000
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	0	0
Prior to reclassification	41,300,000	23,100,000
Other Comprehensive Income (Loss), before Tax	41,300,000	23,100,000
Other Comprehensive Income (Loss), Tax	0	0
Net activity	41,300,000	23,100,000
Stockholders' Equity Attributable to Parent	(69,400,000)	(122,300,000)	(110,700,000)	(145,400,000)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	1,200,000	1,200,000
Tax effect	(200,000)	(300,000)
Prior to reclassification	(500,000)	(200,000)
Other Comprehensive Income (Loss), before Tax	700,000	1,000,000.0
Other Comprehensive Income (Loss), Tax	(200,000)	(300,000)
Net activity	500,000	700,000
Stockholders' Equity Attributable to Parent	(39,700,000)	(43,600,000)	(40,200,000)	(44,300,000)
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	3,400,000	(900,000)
Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	(2,200,000)	2,100,000
Prior to reclassification	37,800,000	18,700,000
Other Comprehensive Income (Loss), before Tax	35,600,000	20,800,000
Other Comprehensive Income (Loss), Tax	(1,300,000)	(400,000)
Net activity	36,900,000	21,200,000
Stockholders' Equity Attributable to Parent	(143,300,000)	(161,300,000)	(180,200,000)	(182,500,000)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of tax	1,000,000.0	900,000
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax effect	800,000	(300,000)
Foreign Exchange Forward [Member] | Available-for-sale Securities and Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other Comprehensive Income (Loss), before Tax	(2,200,000)	(200,000)
Net activity	(1,700,000)	(200,000)
Stockholders' Equity Attributable to Parent	(2,000,000.0)	0	(300,000)	200,000
Foreign Exchange Forward [Member] | Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other Comprehensive Income (Loss), Tax	500,000	0
Interest Rate Swap [Member] | Available-for-sale Securities and Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other Comprehensive Income (Loss), before Tax	5,400,000	1,700,000
Net activity	4,200,000	1,300,000
Stockholders' Equity Attributable to Parent	(31,500,000)	(3,900,000)	(35,700,000)	(5,200,000)
Interest Rate Swap [Member] | Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	2,600,000	(800,000)
Tax effect	600,000	(200,000)
Net of tax	2,000,000.0	(600,000)
Prior to reclassification	8,000,000.0	900,000
Other Comprehensive Income (Loss), Tax	(1,200,000)	(400,000)
Foreign Exchange | Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	800,000	(100,000)
Tax effect	200,000	(100,000)
Net of tax	600,000	0
Prior to reclassification	(1,400,000)	(300,000)
Currency Swap [Member] | Available-for-sale Securities and Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Stockholders' Equity Attributable to Parent			$ 6,700,000	$ 12,200,000
Currency Swap [Member] | Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	0	0
Prior to reclassification	(9,600,000)	(4,800,000)
Other Comprehensive Income (Loss), Tax	2,200,000	1,100,000
Foreign Exchange Contract [Member] | Available-for-sale Securities and Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other Comprehensive Income (Loss), before Tax	(9,600,000)	(4,800,000)
Net activity	(7,400,000)	(3,700,000)
Stockholders' Equity Attributable to Parent	$ (700,000)	$ 8,500,000