Post-effective amendment to a registration statement that is not immediately effective upon filing

Stock-Based Compensation - Narrative (Details)

v3.22.0.1
Stock-Based Compensation - Narrative (Details) - USD ($)
$ / shares in Units, $ in Millions
 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]                  
Profit interests, percent   50.00%              
Unrecognized compensation expense     $ 41.3   $ 41.3        
Expected period for recognition         2 years        
Profit Interest 1                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Profit interests amount   $ 3.2              
Profits interest, threshold price (in dollars per share)   $ 12.0              
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   $ 2.0              
Profits interest, threshold price (in dollars per share)   $ 14.0              
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   $ 3.0              
Profits interest, threshold price (in dollars per share)   $ 16.0              
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           $ 0.0 $ 0.2 $ 0.1  
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%