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Property, Plant and Equipment - Additional Information (Detail) $ in Millions | 12 Months Ended
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Mar. 31, 2020 USD ($) plant | Mar. 31, 2019 USD ($) | Mar. 31, 2018 USD ($)
Property, Plant and Equipment [Line Items] |  |  |
Depreciation expense | $ 125.4 | $ 109.6 | $ 88.9
Asset impairments | 84.4 | 15.9 | 0.0
Property, plant and equipment, net | 1,341.7 | 1,388.4 |
Other impairment charges | 1.2 |  |
Cost of Sales |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Impairment charges related to decision to shut down facility |  | 0.4 |
Other impairment charges | 2.8 | 0.4 | $ 0.7
Shut Down of Summerville, South Carolina Facility |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Impairment charges related to decision to shut down facility | 12.0 |  |
Impairment charge, difference between carrying value and fair value | 22.1 |  |
Costs to sell | 10.1 |  |
Non-Core Assets |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Impairment charges related to decision to shut down facility | $ 29.2 |  |
Number of plants | plant | 4 |  |
North America Fiber Cement |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Asset impairments | $ 41.2 | 2.6 |
Impairment charges related to decision to shut down facility |  | 2.6 |
Other impairment charges | 0.0 |  |
North America Fiber Cement | Cost of Sales |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Other impairment charges | 2.8 |  |
Asia Pacific Fiber Cement |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Asset impairments | 36.3 |  |
Other impairment charges | 1.2 |  |
Asia Pacific Fiber Cement | Penrose Plant Assets |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Property, plant and equipment, net | 2.6 |  |
Asia Pacific Fiber Cement | Exit of Business |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Asset impairments | 14.0 |  |
Impairment charges related to decision to shut down facility | 1.0 |  |
Europe Building Products |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Asset impairments | 5.5 |  |
Other impairment charges | 0.0 |  |
Europe Building Products | Non-Core Assets |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Asset impairments | $ 5.5 |  |
Other Businesses |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Asset impairments |  | 6.1 |
Impairment charges related to decision to shut down facility |  | $ 6.1 |

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