Annual report pursuant to Section 13 and 15(d)

Document and Entity Information

v3.10.0.1
Document and Entity Information - USD ($)
$ in Millions
 12 Months Ended
Sep. 30, 2018
Dec. 10, 2018
May 08, 2018
Document Information [Line Items]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Sep. 30, 2018    
Document Fiscal Year Focus 2018    
Document Fiscal Period Focus FY    
Trading Symbol ROAD    
Entity Registrant Name Construction Partners, Inc.    
Entity Central Index Key 0001718227    
Current Fiscal Year End Date --09-30    
Entity Filer Category Non-accelerated Filer    
Entity Emerging Growth Company true    
Entity Small Business true    
Entity Ex Transition Period false    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Public Float     $ 135
Entity Shell Company false    
Class A Common Stock      
Document Information [Line Items]      
Entity Common Stock, Shares Outstanding (in shares)   11,950,000  
Class B Common Stock      
Document Information [Line Items]      
Entity Common Stock, Shares Outstanding (in shares)   39,464,619