Significant Accounting Policies - Share-based Compensation (Details) - USD ($)	12 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	$ 222,478,000	$ 71,151,000	$ 22,294,000
Income tax benefit recognized on shares-based compensation arrangements	$ 0	$ 4,800,000	$ 700,000
Management Incentive Unit
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Distributions during the period (in shares)	0	0	0
Appreciation Unit
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Distributions during the period (in shares)	0	0	0

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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Number of shares issued under share-based payment arrangement.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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