Annual report pursuant to Section 13 and 15(d)

Cover Page

Cover Page - USD ($)
12 Months Ended
Sep. 30, 2020
Dec. 09, 2020
Mar. 31, 2020
Document Information [Line Items]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Sep. 30, 2020    
Document Fiscal Year Focus 2020    
Document Fiscal Period Focus FY    
Entity Registrant Name Construction Partners, Inc.    
Entity Central Index Key 0001718227    
Current Fiscal Year End Date --09-30    
Entity Filer Category Accelerated Filer    
Entity Emerging Growth Company true    
Entity Ex Transition Period true    
Entity Small Business true    
Trading Symbol ROAD    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Public Float     $ 315,307,621
Entity File Number 001-38479    
Document Annual Report true    
Document Transition Report false    
Entity Shell Company false    
Entity Interactive Data Current Yes    
Title of 12(b) Security Class A common stock, par value $0.001    
City Area Code 334    
Local Phone Number 673-9763    
Security Exchange Name NASDAQ    
Entity Address, State or Province AL    
Entity Address, City or Town Dothan    
Entity Address, Address Line One 290 Healthwest Drive, Suite 2    
Entity Address, Postal Zip Code 36303    
Entity Tax Identification Number 26-0758017    
Entity Incorporation, State or Country Code DE    
Documents Incorporated by Reference Portions of the registrant’s definitive proxy statement to be filed with the Securities and Exchange Commission within 120 days after the registrant’s fiscal year ended September 30, 2020 in connection with the registrant’s 2021 annual meeting of stockholders are incorporated by reference into Part III of this report.    
ICFR Auditor Attestation Flag false    
Class A Common Stock      
Document Information [Line Items]      
Entity Common Stock, Shares Outstanding (in shares)   33,875,884  
Class B Common Stock      
Document Information [Line Items]      
Entity Common Stock, Shares Outstanding (in shares)   17,905,861