Document and Entity Information - shares
6 Months Ended
Oct. 31, 2019
Nov. 30, 2019
Cover [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Oct. 31, 2019  
Document Fiscal Year Focus 2020  
Document Fiscal Period Focus Q2  
Trading Symbol KALV  
Entity Central Index Key 0001348911  
Current Fiscal Year End Date --04-30  
Entity Filer Category Accelerated Filer  
Entity Small Business true  
Entity Emerging Growth Company true  
Entity Ex Transition Period true  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Shell Company false  
Document Quarterly Report true  
Title of 12(b) Security Common Stock, $0.001 par value per share  
Security Exchange Name NASDAQ  
Document Transition Report false  
Entity File Number 001-36830  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 20-0915291  
Entity Address, Address Line One 55 Cambridge Parkway  
Entity Address, Address Line Two Suite 901E  
Entity Address, City or Town Cambridge  
Entity Address, State or Province MA  
Entity Address, Postal Zip Code 02142  
City Area Code 857  
Local Phone Number 999-0075  
Entity Common Stock, Shares Outstanding   17,834,126