Share-Based Compensation - Employee Stock Purchase Plan (Details) - USD ($) $ in Millions	12 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation cost not yet recognized	$ 263.2
Restricted stock units' weighted average remaining expense recognition period (in years)	2 years 10 days
Employee Stock Purchase Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation arrangement by share based payment award, market price offering date percentage	85.00%
Common stock, capital shares reserved for future issuance (in shares)	16,289,436
Share-based compensation arrangement by share-based payment award, number of shares available for grant (in shares)	6,347,253
Stock issued during period, shares, employee stock purchase plans (in shares)	787,284	549,796	828,015
Stock issued during period, value, employee stock purchase plan	$ 55.6	$ 39.6	$ 38.2
Total compensation cost not yet recognized	$ 5.8
Restricted stock units' weighted average remaining expense recognition period (in years)	5 months

Aggregate number of common shares reserved for future issuance.

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