Subsequent events (Details) - shares |
1 Months Ended | 12 Months Ended | |
|---|---|---|---|
Feb. 28, 2019 |
Feb. 28, 2018 |
Dec. 31, 2018 |
|
| Performance-based restricted stock unit awards | |||
| Subsequent events | |||
| Granted (in shares) | 584,000 | ||
| Vesting period | 3 years | ||
| Subsequent events | Executive members | Time-based restricted stock unit awards | |||
| Subsequent events | |||
| Granted (in shares) | 93,000 | ||
| Vesting period | 3 years | ||
| Subsequent events | Executive members | Performance-based restricted stock unit awards | |||
| Subsequent events | |||
| Granted (in shares) | 80,000 | ||
| Subsequent events | Non-executive personnel | Time-based restricted stock unit awards | |||
| Subsequent events | |||
| Granted (in shares) | 205,000 | ||
| Vesting period | 3 years | ||