Annual report pursuant to Section 13 and 15(d)

Subsequent Events (Detail)

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Subsequent Events (Detail) - USD ($)
 1 Months Ended 12 Months Ended
Oct. 21, 2019
Oct. 18, 2019
Oct. 01, 2019
Sep. 30, 2019
Sep. 30, 2019
Sep. 30, 2018
May 15, 2018
Sep. 30, 2017
Jun. 30, 2017
Subsequent Event [Line Items]                  
Long-term debt       $ 50,263,000 $ 50,263,000 $ 63,264,000      
Goodwill       38,546,000 38,546,000 32,919,000   $ 30,600,000  
BBVA Credit Agreement                  
Subsequent Event [Line Items]                  
Maximum borrowing capacity       10,000,000 10,000,000        
Subsequent Event | BBVA Credit Agreement                  
Subsequent Event [Line Items]                  
Maximum borrowing capacity     $ 54,700,000            
Annual maintenance fee   $ 600              
Percentage of fee for issuing letter of credit   0.20%              
Interest Rate Swap                  
Subsequent Event [Line Items]                  
Notional amount             $ 11,000,000.0   $ 25,000,000.0
Line of Credit                  
Subsequent Event [Line Items]                  
Maximum borrowing capacity       30,000,000.0 30,000,000.0        
Line of Credit | BBVA Credit Agreement                  
Subsequent Event [Line Items]                  
Long-term debt       5,000,000.0 5,000,000.0 5,000,000      
Line of Credit | Subsequent Event | BBVA Credit Agreement                  
Subsequent Event [Line Items]                  
Long-term debt     10,000,000            
Senior Notes | BBVA Credit Agreement                  
Subsequent Event [Line Items]                  
Long-term debt       44,700,000 44,700,000 57,300,000      
Interest rate, percentage             3.01%    
Senior Notes | Interest Rate Swap                  
Subsequent Event [Line Items]                  
Notional amount       $ 21,500,000 $ 21,500,000 $ 28,700,000      
Senior Notes | Interest Rate Swap | Subsequent Event | BBVA Credit Agreement                  
Subsequent Event [Line Items]                  
Notional amount     $ 5,900,000            
Interest rate, percentage     1.58%            
Class A Common Stock                  
Subsequent Event [Line Items]                  
Issuance of stock (in shares)         292,534 9,350,000      
Class A Common Stock | Over-Allotment Option                  
Subsequent Event [Line Items]                  
Issuance of stock (in shares)       5,000,000          
Class A Common Stock | Subsequent Event                  
Subsequent Event [Line Items]                  
Share price (in dollars per share) $ 14.25                
Class A Common Stock | Subsequent Event | Over-Allotment Option                  
Subsequent Event [Line Items]                  
Issuance of stock (in shares) 750,000                
HMA Manufacturing Plant And Paving Company | Subsequent Event                  
Subsequent Event [Line Items]                  
Cash payment to acquire business     $ 17,300,000            
Goodwill     $ 6,900,000