Revenue Recognition - Schedule of Disaggregated Revenue by Major Business Line (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Disaggregation Of Revenue [Table]
Total revenue	$ 206,658	$ 221,584	$ 204,974	$ 207,666	$ 207,081	$ 200,563	$ 181,778	$ 180,010	$ 840,883	$ 769,432	$ 593,749
U.S.
Disaggregation Of Revenue [Table]
Total revenue									705,409	665,082	526,685
International
Disaggregation Of Revenue [Table]
Total revenue									135,474	104,350	67,064
Impella Product
Disaggregation Of Revenue [Table]
Total revenue									806,824	741,699	570,870
Service and Other
Disaggregation Of Revenue [Table]
Total revenue									$ 34,059	$ 27,733	$ 22,879