Quarterly report pursuant to Section 13 or 15(d)

Acquisitions - Additional Information (Detail)

v3.19.3
Acquisitions - Additional Information (Detail) - USD ($)
1 Months Ended 3 Months Ended 9 Months Ended 12 Months Ended
Jul. 01, 2019
Apr. 12, 2019
Dec. 13, 2018
Dec. 15, 2015
Mar. 30, 2015
Aug. 31, 2019
May 31, 2019
Sep. 30, 2019
Mar. 31, 2019
Sep. 30, 2018
Jun. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Dec. 31, 2018
Business Acquisition [Line Items]                            
Revenue               $ 27,845,000   $ 24,932,000   $ 74,314,000 $ 73,840,000  
Income before provision for income taxes               $ 6,324,000   $ 5,206,000   14,901,000 $ 16,071,000  
Class B Common Stock                            
Business Acquisition [Line Items]                            
Issuance of Class B shares, Shares           241,624 948 663,000 2,000   6,000      
Cortina Asset Management, LLC                            
Business Acquisition [Line Items]                            
Aggregate purchase amount                       57,824,000    
Equity consideration for SLP acquired               $ 13,800,000       13,800,000    
Revenue               3,182,000       3,182,000    
Income before provision for income taxes               976,000       976,000    
Cash paid on date of acquisition                       35,169,000    
Cash paid on date of acquisition                       17,072,000    
Cortina Asset Management, LLC | General, Administrative and Other                            
Business Acquisition [Line Items]                            
Costs related to acquisition                       1,147,000    
Cortina Asset Management, LLC | Purchase Agreement                            
Business Acquisition [Line Items]                            
Aggregate purchase amount $ 33,577,000                          
Percentage to acquire business in cash   80.00%                        
Additional percentage to acquire business in cash 80.00% 80.00%                        
Business combination consideration partially offset by net closing credits $ 35,072,000                          
Equity consideration for SLP acquired 13,800,000                          
Business combination acquired revenue   $ 13,027,000                        
Cortina Asset Management, LLC | Purchase Agreement | Revenue Greater than or Equal to 95% for July 1, 2020 to June 30, 2021                            
Business Acquisition [Line Items]                            
Business combination contingent consideration first retention payment   3,370,000                        
Cortina Asset Management, LLC | Purchase Agreement | Revenue Equal to 75% or Less for July 1, 2020 to June 30, 2021                            
Business Acquisition [Line Items]                            
Business combination contingent consideration first retention payment   0                        
Cortina Asset Management, LLC | Purchase Agreement | Revenue Between 75% and 95% for July 1, 2020 to June 30, 2021                            
Business Acquisition [Line Items]                            
Business combination contingent consideration first retention payment, minimum   0                        
Business combination contingent consideration first retention payment, maximum   3,370,000                        
Cortina Asset Management, LLC | Purchase Agreement | Revenue Between 85% and 105% for July 1, 2021 to June 30, 2022                            
Business Acquisition [Line Items]                            
Business combination contingent consideration second retention payment, minimum   0                        
Business combination contingent consideration second retention payment, maximum   5,617,000                        
Cortina Asset Management, LLC | Purchase Agreement | Revenue Equal to 85% or Less for July 1, 2021 to June 30, 2022                            
Business Acquisition [Line Items]                            
Business combination contingent consideration second retention payment   0                        
Cortina Asset Management, LLC | Purchase Agreement | Revenue Between 95% and 140% for July 1, 2022 to June 30, 2023                            
Business Acquisition [Line Items]                            
Business combination contingent consideration growth payment, minimum   0                        
Business combination contingent consideration growth payment, maximum   17,222,000                        
Cortina Asset Management, LLC | Purchase Agreement | Revenue Equal to 95% or Less for July 1, 2022 to June 30, 2023                            
Business Acquisition [Line Items]                            
Business combination contingent consideration growth payment   0                        
Cortina Asset Management, LLC | Purchase Agreement | Maximum                            
Business Acquisition [Line Items]                            
Aggregate purchase amount   44,937,000                        
Additional aggregate purchase amount 26,209,000 26,209,000                        
Cortina Asset Management, LLC | Purchase Agreement | Maximum | Revenue Between 85% and 105% for July 1, 2021 to June 30, 2022                            
Business Acquisition [Line Items]                            
Business combination contingent consideration second retention payment   5,617,000                        
Cortina Asset Management, LLC | Purchase Agreement | Maximum | Revenue Between 95% and 140% for July 1, 2022 to June 30, 2023                            
Business Acquisition [Line Items]                            
Business combination contingent consideration growth payment   $ 17,222,000                        
Cortina Asset Management, LLC | Purchase Agreement | SLP                            
Business Acquisition [Line Items]                            
Percentage of business combination consideration issuance   20.00%                        
Additional aggregate purchase amount $ 8,952,000                          
Additional percentage of earn out payment paid in cash 20.00% 20.00%                        
Potential earn-out payments period 4 years 4 years                        
Cortina Asset Management, LLC | Purchase Agreement | SLP | Class B Common Stock                            
Business Acquisition [Line Items]                            
Issuance of Class B shares, Shares 662,713                          
Neosho                            
Business Acquisition [Line Items]                            
Equity consideration for SLP acquired     $ 20,000         1,686,000       1,686,000    
Cash paid on date of acquisition     399,000                 399,000    
Contingent consideration     1,686,000                      
Expected payments on first anniversary of closing date     300,000                      
Earn out payments due in two years     100,000                      
Earn out payments due in three years     100,000                      
Earn out payments due in four years     100,000                      
Earn out payments due in five years     $ 100,000                      
Percentage of product to obtain earn out payment     50.00%                      
Percentage of earn out payment paid in cash     75.00%                      
Percentage of earn out payment paid in equity     25.00%                      
Cappiccille                            
Business Acquisition [Line Items]                            
Equity consideration for SLP acquired               $ 126,000       126,000   $ 231,000
Contingent consideration       $ 354,000                    
Cash paid on date of acquisition       $ 148,000                    
Earn out payments percentage on revenue remainder of fiscal year       19.00%                    
Earn out payments percentage on revenue due in two years       19.00%                    
Earn out payments percentage on revenue due in three years       19.00%                    
Earn out payments percentage on revenue due in four years       19.00%                    
Earn out payments percentage on revenue due thereafter       19.00%                    
Jamison                            
Business Acquisition [Line Items]                            
Equity consideration for SLP acquired         $ 3,562,000                  
Contingent consideration         1,429,000             $ 204,000   $ 524,000
Cash paid on date of acquisition         $ 3,550,000                  
Earn out payments percentage on EBITDA remainder of fiscal year         20.00%                  
Earn out payments percentage on EBITDA due in two years         20.00%                  
Earn out payments percentage on EBITDA due in three years         20.00%                  
Earn out payments percentage on EBITDA due in four years         20.00%                  
Earn out payments percentage on EBITDA due in five years         20.00%                  
Earn Out Payments Percentage On EBITDA Due thereafter         20.00%                  
Jamison | Seller Note                            
Business Acquisition [Line Items]                            
Promissory note issued         $ 394,000                  
Interest on principal amount         5.00%                  
Jamison | Principals Notes                            
Business Acquisition [Line Items]                            
Promissory note issued         $ 1,771,000                  
Interest on principal amount         5.00%