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Stock-Based Compensation - Narrative (Details) - USD ($) |  |  | 2 Months Ended | 4 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | --- | ---
Oct. 19, 2021 | Jun. 17, 2021 | Dec. 31, 2021 | Oct. 19, 2021 | Dec. 31, 2021 | Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2019 | Aug. 13, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Common stock, shares outstanding (in shares) |  |  | 18,750,000 |  | 18,750,000 |  |  |  |
Profit interests, percent |  | 50.00% |  |  |  |  |  |  |
Unrecognized compensation expense |  |  | $ 41,300,000 |  | $ 41,300,000 |  |  |  |
Expected period for recognition |  |  |  |  | 2 years |  |  |  |
Profit Interest 1 |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Profit interests amount |  | $ 3,200,000 |  |  |  |  |  |  |
Profits interest, threshold price (in dollars per share) |  | $ 12 |  |  |  |  |  |  |
Weighted average grant date profit interests fair value (in dollars per share) |  | $ 8.03 |  |  |  |  |  |  |
Profit Interest 2 |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Profit interests amount |  | $ 2,000,000 |  |  |  |  |  |  |
Profits interest, threshold price (in dollars per share) |  | $ 14 |  |  |  |  |  |  |
Weighted average grant date profit interests fair value (in dollars per share) |  | $ 6.83 |  |  |  |  |  |  |
Profit Interest 3 |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Profit interests amount |  | $ 3,000,000 |  |  |  |  |  |  |
Profits interest, threshold price (in dollars per share) |  | $ 16 |  |  |  |  |  |  |
Weighted average grant date profit interests fair value (in dollars per share) |  | $ 5.74 |  |  |  |  |  |  |
Thomas Logan (CEO) |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Shares issued (in shares) |  | 3,200,000 |  |  |  |  |  |  |
Brian Schopfer (CFO) |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Shares issued (in shares) |  | 700,000 |  |  |  |  |  |  |
Lawrence Kingsley (Chairman of Board) |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Shares issued (in shares) |  | 4,200,000 |  |  |  |  |  |  |
Minimum |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Number of trading days for determining the value per share |  | 20 days |  |  |  |  |  |  |
Maximum |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Number of trading days for determining the value per share |  | 30 days |  |  |  |  |  |  |
Class A Common Stock |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Common stock, shares outstanding (in shares) |  |  | 199,523,292 |  | 199,523,292 |  |  |  | 18,750,000
2021 Omnibus Incentive Plan |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Common stock, capital shares reserved for future issuance |  |  | 19,952,329 |  | 19,952,329 |  |  |  |
2021 Omnibus Incentive Plan | Class A Common Stock |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Common stock, capital shares reserved for future issuance | 19,952,329 |  |  | 19,952,329 |  |  |  |  |
Common stock outstanding, ownership percentage | 3.00% |  |  | 3.00% |  |  |  |  |
Common stock, shares outstanding (in shares) | 9,976,164 |  |  | 9,976,164 |  |  |  |  |
Restricted Stock |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Requisite service period | 4 years |  |  |  |  |  |  |  |
Shares issued (in shares) |  |  |  | 0 |  | 0 |  |  |
Shares reissued |  |  |  | 0 |  | 144,219 |  |  |
Share-based compensation expense |  |  |  |  |  | $ 0 | $ 200,000 | $ 100,000 |
Restricted Stock | Minimum |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Requisite service period |  |  |  |  | 3 years |  |  |  |
Restricted Stock | Maximum |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Requisite service period |  |  |  |  | 4 years |  |  |  |
Restricted Stock | Ordinary A shares of Mirion TopCo common stock |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Shares issued (in shares) | 1,483,795 |  |  |  |  |  |  |  |
PSUs |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Expected period for recognition |  |  | 3 years |  |  |  |  |  |
PSUs | Minimum |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Award agreement's target contingent on performance level compensation range, percentage | 0.00% |  |  | 0.00% |  |  |  |  |
PSUs | Maximum |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Award agreement's target contingent on performance level compensation range, percentage | 100.00% |  |  | 100.00% |  |  |  |  |

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