Income taxes - Schedule of Reconciliation of Federal Statutory Rate to Company's Effective Tax Rate (Details) |
3 Months Ended | 12 Months Ended | ||
|---|---|---|---|---|
Mar. 31, 2019 |
Mar. 31, 2020 |
Dec. 31, 2018 |
Dec. 31, 2017 |
|
| Income Tax Disclosure [Abstract] | ||||
| Federal statutory rate | 21.00% | 21.00% | 21.00% | 35.00% |
| Federal tax deferred rate change | 0.000 | 0.000 | 0.000 | (0.538) |
| State tax, net of federal benefit | 1.20% | 3.70% | 2.60% | 0.60% |
| State tax deferred rate change, net of federal benefit | 0.00% | 0.10% | 0.90% | 0.90% |
| Nondeductible business expenses | (0.10%) | 0.80% | 1.40% | 0.00% |
| Provision-to-return adjustment | 0.00% | 0.00% | (3.90%) | 0.00% |
| Uncertain tax positions | (0.10%) | (0.20%) | (1.30%) | (1.70%) |
| Stock based compensation | (6.10%) | (0.40%) | (8.60%) | (28.10%) |
| Others | (0.50%) | 0.70% | 1.40% | (1.90%) |
| Effective tax rate | 15.40% | 25.70% | 13.50% | (49.00%) |