Goodwill, In-Process Research and Development and Other Assets - Additional Information (Detail)	3 Months Ended	6 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)
Goodwill [Line Items]
Goodwill	$ 31,727,000	$ 31,727,000	$ 32,601,000
Accumulated impairment loss, goodwill	0	0
In-process research and development	14,800,000	14,800,000	15,208,000
Accumulated impairment losses on IPR&D assets	0	0
Aggregate carrying amount of other investments	78,836,000	78,836,000	80,779,000
Equity method investment	3,000,000	3,000,000
Other intangible assets and other	5,098,000	5,098,000	4,336,000
License Manufacturing Rghts to Technology
Goodwill [Line Items]
Other intangible assets and other	3,600,000	$ 3,600,000
Other Intangible Assets
Goodwill [Line Items]
Intangible asset, amortized useful life		15 years
Shockwave Medical
Goodwill [Line Items]
Investment in affiliate			25,000,000.0
Fair value of investment	50,200,000	$ 50,200,000	56,200,000
Pre-tax unrealized losses on investment	(45,600,000)	(5,900,000)
Medical Device Companies
Goodwill [Line Items]
Aggregate carrying amount of other investments	4,000,000.0	4,000,000.0
Equity method investment	3,000,000.0	3,000,000.0
ECP Entwicklungsgesellschaft mbH
Goodwill [Line Items]
In-process research and development	$ 14,800,000	$ 14,800,000	$ 15,200,000
ECP Entwicklungsgesellschaft mbH | Measurement Input, Discount Rate
Goodwill [Line Items]
Fair value inputs, discount rate	0.21	0.21