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Summary of Significant Accounting Policies - Additional Information (Detail) $ in Millions | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Sep. 30, 2019 USD ($) | Mar. 31, 2020 USD ($) director shares | Mar. 31, 2019 USD ($) shares | Mar. 31, 2018 USD ($) shares | Apr. 01, 2019 USD ($) | Apr. 01, 2018 USD ($)
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Intangible assets, net |  | $ 166.7 | $ 174.4 |  |  |
Goodwill |  | $ 196.9 | 201.1 | $ 4.9 |  |
Ownership interest rate percentage (as percent) |  | 100.00% |  |  |  |
Cumulative effect of new accounting principle in period of adoption |  |  |  |  | $ 0.2 | $ 1,160.3
Equity awards vested percentage after first year |  | 25.00% |  |  |  |
Equity awards vested percentage after second year |  | 25.00% |  |  |  |
Equity awards vested percentage after third year |  | 50.00% |  |  |  |
Reported free cash flow percentage |  | 35.00% |  |  |  |
Operating lease right-of-use-assets |  | $ 40.5 | 0.0 |  |  |
Operating lease liability |  | $ 55.7 |  |  |  |
Understatement of Cash Flows from Operating Activities |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Payments to AICF | $ 8.0 |  |  |  |  |
Reported Free Cash Flow |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Payments to AICF | $ 100.9 |  |  |  |  |
Understatement of Net Cash Used in Investing and Operating Activities |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Amount of error |  |  | $ 16.4 | $ 6.5 |  |
Accounting Standards Update 2016-02 |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Cumulative effect of new accounting principle in period of adoption |  |  |  |  | 0.2 |
Operating lease right-of-use-assets |  |  |  |  | 79.7 |
Operating lease liability |  |  |  |  | $ 82.0 |
Restricted Stock Units (RSUs) [Member] |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Potential diluted common shares outstanding | shares |  | 0 | 0 | 0 |  |
Contingent Shares Not Expected To Vest [Member] |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Potential diluted common shares outstanding | shares |  | 1,500,000 | 2,200,000 | 1,600,000 |  |
AICF Funding |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Ownership interest rate percentage (as percent) |  | 0.00% |  |  |  |
AICF Funding |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Number of directors appointed by Company | director |  | 3 |  |  |  |
AICF Funding | New South Wales, Australia [Member] |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Number of directors appointed by NSW government | director |  | 2 |  |  |  |
Minimum |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life |  | 2 years |  |  |  |
Maximum |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life |  | 13 years |  |  |  |

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