Condensed Consolidated Statements of Shareholders' Equity (unaudited) Statement - USD ($)	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Treasury Stock [Member]
Common Stock, Shares, Outstanding, Beginning Balance at Sep. 30, 2018		88,457,634
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Beginning Balance at Sep. 30, 2018	$ 1,616,200,000	$ 4,400,000	$ 602,900,000	$ 1,876,200,000	$ (113,000,000.0)	$ (754,300,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect on Retained Earnings, Net of Tax | Accounting Standards Update 2014-09 [Member]	(4,900,000)			(4,900,000)
Cumulative Effect on Retained Earnings, Net of Tax | Accounting Standards Update 2016-16 [Member]	(5,600,000)			(5,600,000)
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification				5,400,000	(5,400,000)
Net Income (Loss) Attributable to Parent	91,700,000			91,700,000
Other Comprehensive Income (Loss), Net of Tax	(21,900,000)				(21,900,000)
Dividends	27,400,000		(200,000)	27,600,000
Payment, Tax Withholding, Share-based Payment Arrangement	(4,000,000.0)					(4,000,000.0)
Payments for Repurchase of Common Stock	(75,000,000.0)					(75,000,000.0)
Share-based Compensation on Equity-Classified Awards	16,900,000		16,900,000
Stock Issued During Period, Value, Stock Options Exercised	(8,600,000)		(2,000,000.0)			(6,600,000)
APIC, Share-based Payment Arrangement, Restricted Stock Unit, Increase for Cost Recognition			(4,700,000)
Stock Issued During Period, Value, Restricted Stock Award, Gross						4,700,000
Stock Issued During Period, Value, Employee Stock Purchase Plan	4,200,000		2,600,000			1,600,000
Payments for Repurchase of Common Stock	$ (75,000,000.0)
Other Comprehensive Income (Loss), Tax					1,500,000
Common Stock, Dividends, Per Share, Cash Paid	$ 0.41
Common Stock, Shares, Outstanding, Ending Balance at Mar. 31, 2019		88,457,634
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance at Mar. 31, 2019	$ 1,598,800,000	$ 4,400,000	619,900,000	1,935,200,000	(140,300,000)	(820,400,000)
Common Stock, Shares, Outstanding, Beginning Balance at Dec. 31, 2018		88,457,634
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Beginning Balance at Dec. 31, 2018	1,551,500,000	$ 4,400,000	606,900,000	1,899,900,000	(135,300,000)	(824,400,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	49,500,000
Net Income (Loss) Attributable to Parent	49,500,000			49,500,000
Other Comprehensive Income (Loss), Net of Tax	(5,000,000.0)				(5,000,000.0)
Dividends	(14,100,000)		(100,000)	(14,200,000)
Payment, Tax Withholding, Share-based Payment Arrangement	(500,000)					(500,000)
Share-based Compensation on Equity-Classified Awards	11,100,000		11,100,000
Stock Issued During Period, Value, Stock Options Exercised	4,000,000.0		(1,000,000.0)			(3,000,000.0)
APIC, Share-based Payment Arrangement, Restricted Stock Unit, Increase for Cost Recognition			(700,000)
Stock Issued During Period, Value, Restricted Stock Award, Gross						700,000
Stock Issued During Period, Value, Employee Stock Purchase Plan	$ 2,300,000		1,500,000			800,000
Other Comprehensive Income (Loss), Tax					(1,400,000)
Common Stock, Dividends, Per Share, Cash Paid	$ 0.21
Common Stock, Shares, Outstanding, Ending Balance at Mar. 31, 2019		88,457,634
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance at Mar. 31, 2019	$ 1,598,800,000	$ 4,400,000	619,900,000	1,935,200,000	(140,300,000)	(820,400,000)
Common Stock, Shares, Outstanding, Beginning Balance at Sep. 30, 2019	66,625,011	88,457,634
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Beginning Balance at Sep. 30, 2019	$ 1,573,300,000	$ 4,400,000	637,400,000	1,967,400,000	(182,500,000)	(853,400,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	86,700,000
Net Income (Loss) Attributable to Parent	86,700,000
Other Comprehensive Income (Loss), Net of Tax	(41,100,000)				(41,100,000)
Dividends	(28,700,000)		(200,000)	(28,900,000)
Payment, Tax Withholding, Share-based Payment Arrangement	(15,800,000)					(15,800,000)
Payments for Repurchase of Common Stock	(54,100,000)					(54,100,000)
Share-based Compensation on Equity-Classified Awards	18,500,000		18,500,000
Stock Issued During Period, Value, Stock Options Exercised	(5,700,000)		(1,700,000)			(4,000,000.0)
APIC, Share-based Payment Arrangement, Restricted Stock Unit, Increase for Cost Recognition			(16,100,000)
Stock Issued During Period, Value, Restricted Stock Award, Gross	100,000					16,200,000
Stock Issued During Period, Value, Employee Stock Purchase Plan	4,300,000		2,700,000			1,600,000
Stock Issued During Period, Shares, Employee Stock Purchase Plans		0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period		0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period		0
Payments for Repurchase of Common Stock	$ 54,100,000
Other Comprehensive Income (Loss), Tax					9,800,000
Common Stock, Dividends, Per Share, Cash Paid	$ 0.43
Common Stock, Shares, Outstanding, Ending Balance at Mar. 31, 2020	66,527,730	88,457,634
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance at Mar. 31, 2020	$ 1,548,900,000	$ 4,400,000	644,400,000	2,025,200,000	(223,600,000)	(901,500,000)
Common Stock, Shares, Outstanding, Beginning Balance at Dec. 31, 2019		88,457,634
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Beginning Balance at Dec. 31, 2019	1,619,000,000.0	$ 4,400,000	632,700,000	1,993,100,000	(161,300,000)	(849,900,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	46,900,000
Net Income (Loss) Attributable to Parent	46,900,000
Other Comprehensive Income (Loss), Net of Tax	(62,300,000)				(62,300,000)
Dividends	(14,600,000)		(200,000)	(14,800,000)
Payment, Tax Withholding, Share-based Payment Arrangement	(700,000)					(700,000)
Payments for Repurchase of Common Stock	(54,100,000)					(54,100,000)
Share-based Compensation on Equity-Classified Awards	10,200,000		10,200,000
Stock Issued During Period, Value, Stock Options Exercised	(2,000,000.0)		(600,000)			(1,400,000)
APIC, Share-based Payment Arrangement, Restricted Stock Unit, Increase for Cost Recognition			(700,000)
Stock Issued During Period, Value, Restricted Stock Award, Gross	100,000					800,000
Stock Issued During Period, Value, Employee Stock Purchase Plan	$ 2,400,000		1,400,000			1,000,000.0
Other Comprehensive Income (Loss), Tax					(9,400,000)
Common Stock, Dividends, Per Share, Cash Paid	$ 0.22
Common Stock, Shares, Outstanding, Ending Balance at Mar. 31, 2020	66,527,730	88,457,634
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance at Mar. 31, 2020	$ 1,548,900,000	$ 4,400,000	$ 644,400,000	$ 2,025,200,000	$ (223,600,000)	$ (901,500,000)