Annual report pursuant to Section 13 and 15(d)


Cover - USD ($)
$ in Millions
12 Months Ended
Sep. 30, 2023
Dec. 11, 2023
Mar. 31, 2023
Cover [Abstract]      
Document Type 10-K    
Amendment Flag false    
Document Annual Report true    
Document Transition Report false    
Document Period End Date Sep. 30, 2023    
Document Fiscal Period Focus FY    
Document Fiscal Year Focus 2023    
Current Fiscal Year End Date --09-30    
Entity File Number 001-35570    
Entity Central Index Key 0001106838    
Entity Tax Identification Number 20-2932652    
Entity Incorporation, State or Country Code DE    
Entity Address, Address Line One 100 Overlook Center    
Entity Address, Address Line Two Suite 102    
Entity Address, City or Town Princeton    
Entity Address, State or Province NJ    
Entity Address, Postal Zip Code 08540    
City Area Code (609)    
Local Phone Number 375-2227    
Title of 12(b) Security Common Stock, $0.0001 par value per share    
Trading Symbol SONN    
Security Exchange Name NASDAQ    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Non-accelerated Filer    
Entity Small Business true    
Entity Emerging Growth Company false    
Entity Shell Company false    
Entity Public Float     $ 7.3
Entity Common Stock, Shares Outstanding   3,069,516  
Documents Incorporated by Reference [Text Block] None    
ICFR Auditor Attestation Flag false    
Document Financial Statement Error Correction [Flag] false    
Auditor Firm ID 185    
Auditor Name KPMG LLP    
Auditor Location Philadelphia, Pennsylvania