Income taxes - Narrative (Details) - USD ($) $ in Thousands |
Dec. 31, 2020 |
Dec. 31, 2019 |
|---|---|---|
| Business Acquisition [Line Items] | ||
| Acquired net operating losses | $ 1,753 | $ 0 |
| Franklin Financial Network, Inc. | ||
| Business Acquisition [Line Items] | ||
| Acquired net operating losses | $ 8,346 |