Construction Partners, Inc. Quarterly report pursuant to Section 13 or 15(d)

Quarterly report pursuant to Section 13 or 15(d)

Subsequent Events - Additional Information (Detail)

Subsequent Events - Additional Information (Detail)				3 Months Ended	6 Months Ended	12 Months Ended
Subsequent Events - Additional Information (Detail)	May 24, 2018 USD ($) $ / shares shares	May 15, 2018 USD ($) Plant Mineral_Property	May 08, 2018 USD ($) $ / shares shares	Mar. 31, 2018 USD ($) $ / shares shares	Mar. 31, 2018 USD ($) $ / shares shares	Sep. 30, 2017 USD ($) $ / shares shares	Apr. 23, 2018 $ / shares shares	Apr. 19, 2018 USD ($) Installments
Subsequent Event [Line Items]
Common stock par value \| $ / shares				$ 0.001	$ 0.001	$ 0.001
Common stock shares issued \| shares				44,987,574	44,987,574	44,987,574
Common stock shares authorized \| shares				126,000,000	126,000,000	126,000,000
Common stock shares outstanding \| shares				41,817,541	41,817,541	41,691,541
Other current receivables				$ 3,900,000	$ 3,900,000
Other non current receivables				10,900,000	10,900,000
Subsidiaries [Member] \| Settlement Agreement [Member]
Subsequent Event [Line Items]
Gain related to litigation settlement before tax				14,803,000	14,803,000
Other Current Assets [Member]
Subsequent Event [Line Items]
Offering Cost reflected as capitalized equity issuance costs				4,000,000		$ 2,200,000
Scruggs Company [Member]
Subsequent Event [Line Items]
Business acquisitions pro forma revenue				0	0
Business acquisition pro forma results of operations				$ 0	$ 0
Subsequent Event [Member]
Subsequent Event [Line Items]
Share price \| $ / shares	$ 12.00
Subsequent Event [Member] \| Subsidiaries [Member] \| Settlement Agreement [Member]
Subsequent Event [Line Items]
Settlement agreements, receivable								$ 15,700,000
Settlement agreements, number of equal installments \| Installments								4
Subsequent Event [Member] \| Class A and Class B Common Stock [Member]
Subsequent Event [Line Items]
Common stock par value \| $ / shares							$ 0.001
Subsequent Event [Member] \| Common Class B [Member]
Subsequent Event [Line Items]
Conversion rate to reclassify common stock to class B shares							25.2
Common stock shares issued \| shares	39,217,537		39,567,537				41,817,537
Common stock shares authorized \| shares							100,000,000
Conversion of Common stock B into shares of common stock A \| shares	350,000		2,250,000
Common stock shares outstanding \| shares	39,217,537		39,567,537
Subsequent Event [Member] \| Common Class A [Member]
Subsequent Event [Line Items]
Common stock shares authorized \| shares							400,000,000
Common stock shares issued \| shares	700,000		11,250,000
Share price \| $ / shares			$ 12.00
Subsequent Event [Member] \| Common Class A [Member] \| Directly Sold by The Company [Member]
Subsequent Event [Line Items]
Common stock shares issued \| shares	350,000		9,000,000
Proceeds from issuance initial public offering	$ 3,900,000		$ 100,400,000
Underwriting discounts and commissions	$ 300,000		7,600,000
Estimated offering expenses			$ 5,800,000
Subsequent Event [Member] \| Common Class A [Member] \| Common Class B Shareholders [Member]
Subsequent Event [Line Items]
Common stock shares issued \| shares	350,000		2,250,000
Subsequent Event [Member] \| Scruggs Company [Member]
Subsequent Event [Line Items]
Business acquisition percentage of interest acquired		100.00%
Number of hot mix asphalt plants acquired \| Plant		3
Number of aggregate mines acquired \| Mineral_Property		3
Number of industrial plant acquired \| Plant		1
Business acquisition, purchase price		$ 51,100,000
Subsequent Event [Member] \| Scruggs Company [Member] \| Compass Term Loan [Member]
Subsequent Event [Line Items]
Business acquisition, term loan borrowing		22,000,000
Debt Instrument, Face Amount		50,000,000
Subsequent Event [Member] \| Scruggs Company [Member] \| Compass Term Loan [Member] \| Interest Rate Swap [Member]
Subsequent Event [Line Items]
Swap agreement, notional amount		$ 11,000,000
Term Loan, fixed percentage rate		3.01%