Quarterly report pursuant to Section 13 or 15(d)

Stock options and restricted stock (Details)

v3.10.0.1
Stock options and restricted stock (Details) - USD ($)
3 Months Ended 9 Months Ended 12 Months Ended
May 17, 2018
Feb. 07, 2018
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Allocated share-based compensation expense     $ 205,520 $ 156,502 $ 621,699 $ 486,740  
Antidilutive securities excluded from computation of earnings per share, amount (in shares)         600 144,064  
Stock Options              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Options exercised (in shares)         85,440   0
Aggregate exercise price of options exercised         $ 1,033,108    
Aggregate noncash exercise price of options exercised         $ 891,255    
Stock Awards | 2015 Stock Awards Plan              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Equity instruments other options, grants in period (in shares)   65,527          
Equity instruments other than options, grants in period, weighted average grant date fair value (in dollars per share)   $ 12.47          
Period after option grant before options can be exercised (in years)   1 year          
Stock Awards | 2015 Stock Awards Plan | Minimum              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Annual vesting rate (percent)   20.00%          
Number of additional shares authorized, up to (in shares) 250,000            
Stock Awards | 2015 Stock Awards Plan | Maximum              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Annual vesting rate (percent)   33.00%          
Number of additional shares authorized, up to (in shares) 500,000