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Business Combinations and Acquisitions - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions |  | 1 Months Ended | 2 Months Ended | 4 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | ---
Oct. 20, 2021 | Feb. 28, 2021 | Dec. 31, 2021 | Oct. 19, 2021 | Jun. 30, 2021 | Jun. 30, 2020
Business Combination, Separately Recognized Transactions [Line Items] |  |  |  |  |  |
Payments to acquire businesses gross | $ 1,300.0 |  |  |  |  |
Statutory income tax rate (as a percent) |  |  | 21.00% |  | 25.00% | 25.00%
Intermediate Co |  |  |  |  |  |
Business Combination, Separately Recognized Transactions [Line Items] |  |  |  |  |  |
Payments to acquire businesses gross | $ 1,300.0 |  |  |  |  |
Business acquisition share price (in dollars per share) | $ 10.00 |  |  |  |  |
Mirion TopCo |  |  |  |  |  |
Business Combination, Separately Recognized Transactions [Line Items] |  |  |  |  |  |
Pro forma adjustments |  |  | $ 2.2 | $ 26.2 |  |
Mirion TopCo | Fair Value Adjustment to Inventory |  |  |  |  |  |
Business Combination, Separately Recognized Transactions [Line Items] |  |  |  |  |  |
Pro forma adjustments |  |  | 15.8 | 15.8 | $ 15.8 |
Mirion TopCo | Acquisition-related Costs |  |  |  |  |  |
Business Combination, Separately Recognized Transactions [Line Items] |  |  |  |  |  |
Pro forma adjustments |  |  | 28.4 | $ 28.4 | 28.4 |
CIRS | Medical |  |  |  |  |  |
Business Combination, Separately Recognized Transactions [Line Items] |  |  |  |  |  |
Transaction expenses |  |  | $ 0.4 |  |  |
SNC | Medical |  |  |  |  |  |
Business Combination, Separately Recognized Transactions [Line Items] |  |  |  |  |  |
Payments to acquire businesses gross |  | $ 261.9 |  |  |  |
Transaction expenses |  |  |  |  | 1.2 |
Biodex and SNC | Fair Value Adjustment to Inventory |  |  |  |  |  |
Business Combination, Separately Recognized Transactions [Line Items] |  |  |  |  |  |
Pro forma adjustments |  |  |  |  | 5.2 | $ 5.2
Biodex and SNC | Acquisition-related Costs |  |  |  |  |  |
Business Combination, Separately Recognized Transactions [Line Items] |  |  |  |  |  |
Pro forma adjustments |  |  |  |  | 4.8 | 4.8
Biodex and SNC | Reduction In Revenues Due To The Elimination Of Deferred Contract Revenue |  |  |  |  |  |
Business Combination, Separately Recognized Transactions [Line Items] |  |  |  |  |  |
Pro forma adjustments |  |  |  |  | $ 14.8 | $ 14.8
Class A Common Stock | Intermediate Co |  |  |  |  |  |
Business Combination, Separately Recognized Transactions [Line Items] |  |  |  |  |  |
Business acquisition equity interest issued or issuable (in shares) | 30,401,902 |  |  |  |  |
Class B Common Stock | Intermediate Co |  |  |  |  |  |
Business Combination, Separately Recognized Transactions [Line Items] |  |  |  |  |  |
Business acquisition equity interest issued or issuable (in shares) | 8,560,540 |  |  |  |  |

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