Stock incentive plan (Details Textual) - USD ($)
|
3 Months Ended |
9 Months Ended |
Sep. 30, 2017 |
Jun. 30, 2017 |
Jun. 30, 2016 |
Sep. 30, 2017 |
Sep. 30, 2016 |
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
|
|
| Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options |
$ 301,676
|
|
|
$ 301,676
|
|
| Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition |
|
|
|
1 year 11 months 26 days
|
|
| Allocated Share-based Compensation Expense |
|
|
|
$ 102,000
|
$ 156,000
|
| Restricted Stock [Member] |
|
|
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
|
|
| Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options |
$ 487,374
|
|
|
$ 487,374
|
$ 775,575
|
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period |
5,450
|
600
|
4,000
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value |
$ 31.00
|
$ 28.83
|
$ 20.00
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Beginning Balance |
28,437
|
|
|
28,437
|
51,665
|
| Stock Incentive Plan 2006 [Member] |
|
|
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized |
48,750
|
|
|
48,750
|
|
| Stock Incentive Plan 2015 [Member] |
|
|
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized |
60,000
|
|
|
60,000
|
|