Annual report pursuant to Section 13 and 15(d)

Common Stock and Options - Narrative (Details)

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Common Stock and Options - Narrative (Details) - USD ($)
1 Months Ended 3 Months Ended 12 Months Ended
Sep. 07, 2018
Dec. 31, 2016
Nov. 30, 2017
Sep. 30, 2016
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2016
May 31, 2017
Mar. 31, 2017
Jan. 27, 2017
Sep. 30, 2015
Sep. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Number of shares authorized to be repurchased (up to) (in shares)           7,000,000   2,000,000 5,000,000   170,000 105,000
Total stock compensation expense         $ 2,613,000 $ 1,653,000 $ 924,000          
Employee stock options granted (in shares)       0 300,000 750,000 0          
Restricted Shares                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Restricted shares of common stock awarded (in shares)         5,000 0 0          
Weighted average fair value (in dollars per share)         $ 31.95 $ 0.00 $ 0.00          
Total stock compensation expense         $ 137,000 $ 264,000 $ 150,000          
Unrecognized compensation costs         172,000 149,000            
Employee Stock Option                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Total stock compensation expense         1,617,000 616,000 $ 0          
Unrecognized compensation costs         $ 2,174,000 $ 2,030,000            
Employee stock options granted (in shares)         300,000 750,000            
Number of shares available for issuance (in shares)       0 675,000 750,000 0          
2015 Plan                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Number of shares authorized to be repurchased (up to) (in shares)                   1,250,000    
2015 Plan | Restricted Shares                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Vesting period     2 years 6 months                  
Restricted shares of common stock awarded (in shares)     5,000                  
Weighted average fair value (in dollars per share)     $ 31.95                  
2015 Plan | Employee Stock Option                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Number of shares available for issuance (in shares)         557,500              
2018 Plan                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Shares issued (in dollars per share) $ 33.60                      
Period following an executive's termination of employment for a number of reasons 18 months                      
Period following an executive's termination of employment without cause 12 months                      
Share price (in dollars per share)         $ 33.80              
2018 Plan | Employee Stock Option                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Weighted average grant date fair value (in dollars per share)         7.40              
2016 Plan                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Shares issued (in dollars per share)   $ 27.15                    
Period of consecutive trading days   20 days                    
Period following an executive's termination of employment without cause   18 months                    
Share price (in dollars per share)         $ 33.80              
2016 Plan | Employee Stock Option                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Weighted average grant date fair value of option grant (in dollars per share)           $ 3.53            
Minimum | 2015 Plan                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Vesting period         1 year              
Maximum | 2015 Plan                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Vesting period         6 years              
Maximum | 2018 Plan                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Share price (in dollars per share)         $ 35.00              
Maximum | 2016 Plan                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Share price (in dollars per share)         $ 60.00              
Chief Executive Officer | 2018 Plan                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Employee stock options granted (in shares) 210,000                      
Chief Executive Officer | 2016 Plan                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Employee stock options granted (in shares)   300,000                    
Chief Financial Officer | 2018 Plan                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Employee stock options granted (in shares) 90,000                      
Board of Directors Chairman | 2016 Plan                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Employee stock options granted (in shares)   225,000                    
Shares forfeited (in shares)   187,500                    
Unrecognized compensation expense         $ 783,000              
Tranche One | 2018 Plan                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Percentage of option price to vest 25.00%                      
Period of consecutive trading days 20 days                      
Amount per share (in dollars per share) $ 35.00                      
Tranche One | 2016 Plan                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Percentage of option price to vest   25.00%                    
Amount per share (in dollars per share)   $ 60.00                    
Tranche Two | 2018 Plan                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Percentage of option price to vest 25.00%                      
Period of consecutive trading days 20 days                      
Amount per share (in dollars per share) $ 40.00                      
Tranche Two | 2016 Plan                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Percentage of option price to vest   25.00%                    
Amount per share (in dollars per share)   $ 75.00                    
Tranche Three | 2018 Plan                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Percentage of option price to vest 25.00%                      
Period of consecutive trading days 20 days                      
Amount per share (in dollars per share) $ 45.00                      
Tranche Three | 2016 Plan                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Percentage of option price to vest   25.00%                    
Amount per share (in dollars per share)   $ 90.00                    
Tranche Four | 2018 Plan                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Percentage of option price to vest 25.00%                      
Period of consecutive trading days 20 days                      
Amount per share (in dollars per share) $ 50.00                      
Tranche Four | 2016 Plan                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Percentage of option price to vest   25.00%                    
Amount per share (in dollars per share)   $ 105.00