Document and Entity Information - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Feb. 10, 2020
Jun. 28, 2019
Document and Entity Information      
Entity Registrant Name KALA PHARMACEUTICALS, INC.    
Entity Central Index Key 0001479419    
Document Type 10-K    
Document Period End Date Dec. 31, 2019    
Amendment Flag false    
Current Fiscal Year End Date --12-31    
Entity Interactive Data Current Yes    
Entity Current Reporting Status Yes    
Entity Filer Category Accelerated Filer    
Entity Small Business true    
Entity Emerging Growth Company true    
Entity Ex Transition Period true    
Entity Common Stock, Shares Outstanding   36,803,874  
Entity Shell Company false    
Document Fiscal Year Focus 2019    
Document Fiscal Period Focus FY    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Public Float     $ 160.1