Acquisitions and Investments - Proforma and Specialty Joint Venture (Details) - USD ($) $ in Thousands	1 Months Ended		12 Months Ended
	Sep. 30, 2018	Jan. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Business Acquisition [Line Items]
Investment in profarma			$ 56,080	$ 0	$ 0
Goodwill	$ 6,664,272		6,706,719	6,705,507	6,664,272
Net deferred tax liabilities			324,845	1,860,195
Loss on consolidation of equity investments			0	0	42,328
Foreign currency translation adjustment from AOCI			$ 0	$ 0	$ (45,941)
Profarma Distribuidora de Produtos Farmaceuticos S.A.
Business Acquisition [Line Items]
Investment in profarma		$ 62,500
Ownership interest in profarma		38.20%
Goodwill		$ 142,000
Estimated fair value of accounts receivable		160,100
Estimated fair value of inventory		190,500
Estimated fair value of accounts payable and accrued expenses		167,700
Assumed short-term debt		209,900
Assumed long-term debt		12,400
Assumed cash		150,800
Noncontrolling interest		168,000
Estimated fair value of the intangible assets acquired, finite-lived		84,600
Net deferred tax liabilities		50,100
Profarma Joint Venture
Business Acquisition [Line Items]
Investment in specialty joint venture	$ 23,600	$ 15,600
Ownership in specialty joint venture	89.90%	64.50%			89.90%
Goodwill		$ 3,500
Estimated fair value of accounts receivable		65,000
Estimated fair value of inventory		29,100
Estimated fair value of accounts payable and accrued expenses		54,300
Assumed short-term debt		32,700
Assumed cash		28,900
Estimated fair value of the intangible assets acquired, finite-lived		$ 4,600
Estimated useful life (in years)		15 years
Loss on consolidation of equity investments					$ 8,800
Gain on remeasurement of Profarma's previously held equity interest					12,400
Customer relationships | Profarma Distribuidora de Produtos Farmaceuticos S.A.
Business Acquisition [Line Items]
Estimated fair value of the intangible assets acquired, finite-lived		$ 25,900
Customer relationships | Profarma Joint Venture
Business Acquisition [Line Items]
Estimated useful life (in years)		15 years
Trade names | Profarma Distribuidora de Produtos Farmaceuticos S.A.
Business Acquisition [Line Items]
Estimated fair value of the intangible assets acquired, finite-lived		$ 58,700
Foreign currency translation
Business Acquisition [Line Items]
Foreign currency translation adjustment from AOCI					$ 45,900
Fair Value, Recurring | Level 2 | Profarma Distribuidora de Produtos Farmaceuticos S.A.
Business Acquisition [Line Items]
Fair value of equity interests		103,100
Fair Value, Recurring | Level 2 | Profarma Joint Venture
Business Acquisition [Line Items]
Fair value of equity interests		$ 31,200
Minimum | Trade names | Profarma Distribuidora de Produtos Farmaceuticos S.A.
Business Acquisition [Line Items]
Estimated useful life (in years)		15 years
Maximum | Trade names | Profarma Distribuidora de Produtos Farmaceuticos S.A.
Business Acquisition [Line Items]
Estimated useful life (in years)		25 years