Earnings per common share - Additional Information (Details) - shares |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2020 |
Sep. 30, 2019 |
Sep. 30, 2020 |
Sep. 30, 2019 |
|
| Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] | ||||
| Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount | 0 | 0 | ||
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number | 6,573 | 6,573 | ||
| Stock Option [Member] | ||||
| Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] | ||||
| Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount | 629 | 550 | 593 | 563 |