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 6 Months Ended 12 Months Ended
Feb. 07, 2018
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Allocated share-based compensation expense   $ 223,979 $ 416,179 $ 210,000 $ 330,000  
Antidilutive securities excluded from computation of earnings per share, amount (in shares)       36,815 144,064  
Stock Options            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Options exercised (in shares)       40,606   0
Aggregate exercise price of options exercised       $ 474,378    
2015 Stock Awards Plan | Stock Awards            
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          
Minimum | 2015 Stock Awards Plan | Stock Awards            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Annual vesting rate (percent) 20.00%          
Maximum | 2015 Stock Awards Plan | Stock Awards            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Annual vesting rate (percent) 33.00%