Stock repurchases (Details) - USD ($) $ in Thousands |
Dec. 31, 2017 |
Apr. 01, 2013 |
|---|---|---|
| Stock repurchases | ||
| Remaining amount authorized for the share repurchase program | $ 5,180 | |
| Maximum | ||
| Stock repurchases | ||
| Amount of common stock approved by the entity for a stock repurchase program | $ 10,000 |