Summary of Significant Accounting Policies (Details) - USD ($)	3 Months Ended					6 Months Ended		12 Months Ended
	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2020	Mar. 31, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017	Oct. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Lease, Liability	$ 77,200,000					$ 77,200,000
Operating Lease, Right-of-Use Asset	72,600,000					72,600,000
Selling and administrative expenses	$ 209,900,000	$ 245,400,000	$ 246,400,000	$ 231,200,000	$ 218,000,000.0	406,700,000		$ 941,000,000.0	$ 891,600,000	$ 874,500,000
Acquisition-related intangible asset amortization		40,100,000	29,300,000	27,300,000	25,700,000	$ 53,800,000	$ 53,000,000.0	122,400,000	106,900,000	108,400,000
Selling and administrative expense, revised		$ 205,300,000	$ 217,100,000	$ 203,900,000	$ 192,300,000		396,200,000	$ 818,600,000	$ 784,700,000	$ 766,100,000
Accounting Standards Update 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Lease, Liability											$ 85,800,000
Operating Lease, Right-of-Use Asset											82,500,000
Deferred Rent Credit, Noncurrent											$ 3,300,000
Accounting Standards Update 2016-16 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect on Retained Earnings, Net of Tax							$ (5,600,000)