Stock-Based Compensation - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Number of options
Number of Options outstanding, Beginning Balance	554,906	545,590	451,668
Number of Options, Granted	284,109	192,700	169,703
Number of Options, Exercised	(24,826)	(171,630)	(62,197)
Number of Options, Forfeited	(22,607)	(11,754)	(11,495)
Number of Options, Expired			2,089
Number of Options outstanding, Ending Balance	791,582	554,906	545,590	451,668
Number of Options, Exerciseable	350,660
Number of Options, Vested and Expected to Vest	777,307
Options outstanding, Weighted Average Remaining Contract Term
Options outstanding, Weighted Average Remaining Contract Term (Years)	7 years 9 months 18 days	8 years	8 years 4 months 24 days	8 years 4 months 24 days
Options exercisable, Weighted Average Remaining Contract Term (Years)	6 years 4 months 24 days
Options vested and expected to vest, Weighted Average Remaining Contract Term (Years)	7 years 9 months 18 days
Weighted average exercise price
Options outstanding, Weighted Average Exercise Price, Beginning Balance	$ 72.31	$ 68.65	$ 62.29
Weighted Average Exercise Price, Granted	57.75	75.17	83.14
Weighted Average Exercise Price, Exercised	57.60	63.66	63.44
Weighted Average Exercise Price, Expired	72.19	75.17	70.22
Weighted Average Exercise Price, Forfeited			18.25
Options outstanding, Weighted Average Exercise Price, Ending Balance	67.55	$ 72.31	$ 68.65	$ 62.29
Options exercisable, Weighted Average Exercise Price	70.65
Weighted Average Exercise Price, Vested and Expected to Vest	$ 67.66
Aggregate intrinsic value
Options outstanding, Aggregate Intrinsic Value, Beginning Balance	$ 1,040	$ 2,679	$ 7,520
Options exercised, aggregate intrinsic value	383	2,707	1,132
Options forfeited, aggregate intrinsic value	88		75
Options expired, aggregate intrinsic value			137
Options outstanding, Aggregate Intrinsic Value, Ending Balance	0	$ 1,040	$ 2,679	$ 7,520
Options exercisable, Aggregate Intrinsic Value	0
Options vested and expected to vest, aggregate intrinsic value	$ 0