| Treasury shares (in thousand shares) |
| Balance at | Balance at | |||||||||||||||
| January 1 | Addition | Decrease | December 31 | |||||||||||||
| 2015 | ||||||||||||||||
| Shares held by subsidiaries | 145,883 | - | - | 145,883 | ||||||||||||
| Shares reserved for bonds conversion | - | 120,000 | - | 120,000 | ||||||||||||
| 145,883 | 120,000 | - | 265,883 | |||||||||||||
| Balance at | Balance at | |||||||||||||||
| January 1 | Addition | Decrease | December 31 | |||||||||||||
| 2016 | ||||||||||||||||
| Shares held by subsidiaries | 145,883 | - | - | 145,883 | ||||||||||||
| Shares reserved for bonds conversion | 120,000 | - | - | 120,000 | ||||||||||||
| 265,883 | - | - | 265,883 | |||||||||||||
| 2017 | ||||||||||||||||
| Shares held by subsidiaries | 145,883 | - | - | 145,883 | ||||||||||||
| Shares reserved for bonds conversion | 120,000 | - | - | 120,000 | ||||||||||||
| 265,883 | - | - | 265,883 | |||||||||||||