Employee Stock Purchase Plan - Summary of Employee Stock Purchase Plan (Detail) - USD ($)	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Employee Stock Purchase Plan [Line Items]
Employee contributions	$ 505,000	$ 503,000	$ 458,000
Shares acquired	2,486,565
Employee Stock Purchase Plan [Member]
Employee Stock Purchase Plan [Line Items]
Shares acquired	8,451	8,271	8,976
Average purchase price	$ 59.70	$ 59.55	$ 49.78