v3.26.1
Stock-Based Compensation - Stock Option Activity (Details) - Employee Stock Option - $ / shares
 6 Months Ended 12 Months Ended
Jun. 30, 2026
Dec. 31, 2025
Shares    
Options outstanding at beginning of the period 9,134,278  
Granted 2,588,670  
Exercised (41,894)  
Canceled (250,328)  
Options outstanding at the end of the period 11,430,726 9,134,278
Options vested and expected to vest at the end of the period 11,288,830  
Options exercisable at the end of the period 6,194,728  
Shares available for grant under the Celldex Therapeutics, Inc. 2021 Omnibus Equity Incentive Plan (as amended, effective as of June 25, 2026) at June 30, 2026 3,686,494  
Weighted Average Exercise Price Per Share    
Options outstanding at beginning of the period $ 26.49  
Granted 33.83  
Exercised 22.3  
Canceled 42.97  
Options outstanding at the end of the period 27.8 $ 26.49
Options vested and expected to vest at the end of the period 27.77  
Options exercisable at the end of the period $ 25.6  
Weighted Average Remaining Contractual Term (In Years)    
Options outstanding at the beginning of the period 7 years 6 months 7 years 1 month 6 days
Options vested and expected to vest at the end of the period 7 years 4 months 24 days  
Options exercisable at the end of the period 6 years