| Balance as of 31 December 2018 | 98 | (1,170) | 60,397 | 1,680,978 | 99,874 | 1,840,177 | 151,642 | 1,991,819 |
| Effect of changes in accounting policies (Note 4 ) | - | - | - | (14,565) | - | (14,565) | - | (14,565) |
| Balance as of 1 January 2019 | 98 | (1,170) | 60,397 | 1,666,413 | 99,874 | 1,825,612 | 151,642 | 1,977,254 |
| Profit for the period | - | - | - | 400,201 | - | 400,201 | 21,887 | 422,088 |
| Other comprehensive (loss) / income | | | | | | | | |
| Currency translation differences | - | - | - | - | (18,752) | (18,752) | (10,922) | (29,674) |
| Cash flow hedge, net of tax | - | - | - | - | 319 | 319 | - | 319 |
| Remeasurement of provision for post-employment benefits | - | - | - | - | (2,411) | (2,411) | - | (2,411) |
| Other comprehensive loss | - | - | - | - | (319) | (319) | - | (319) |
| Total comprehensive income / (loss) for the period | - | - | - | 400,201 | (21,163) | 379,038 | 10,965 | 390,003 |
| Transactions with shareholders, recorded in equity | | | | | | | | |
| Dividends to equity holders | - | - | - | (123,091) | - | (123,091) | (6,616) | (129,707) |
| Transactions with shareholder (Note 11 ) | - | - | (24,353) | - | - | (24,353) | - | (24,353) |
| Total transactions with shareholders | - | - | (24,353) | (123,091) | - | (147,444) | (6,616) | (154,060) |
| Balance as of 31 December 2019 | 98 | (1,170) | 36,044 | 1,943,523 | 78,711 | 2,057,206 | 155,991 | 2,213,197 |
| Balance as of 1 January 2018 | 98 | (1,170) | 62,256 | 1,431,931 | 60,142 | 1,553,257 | 105,876 | 1,659,133 |
| Profit for the period | - | - | - | 376,667 | - | 376,667 | 24,326 | 400,993 |
| Other comprehensive income | | | | | | | | |
| Currency translation differences | - | - | - | - | 25,007 | 25,007 | 11,930 | 36,937 |
| Cash flow hedge, net of tax | - | - | - | - | 14,630 | 14,630 | - | 14,630 |
| Other comprehensive income | - | - | - | - | 95 | 95 | - | 95 |
| Total comprehensive income for the period | - | - | - | 376,667 | 39,732 | 416,399 | 36,256 | 452,655 |
| Transactions with shareholders, recorded in equity | | | | | | | | |
| Dividends to equity holders | - | - | - | (127,620) | - | (127,620) | (11,769) | (139,389) |
| Transaction under common control | - | - | (2,819) | - | - | (2,819) | - | (2,819) |
| Change of non-controlling interest in subsidiaries (Note 38) | - | - | 960 | - | - | 960 | 21,279 | 22,239 |
| Total transactions with shareholders | - | - | (1,859) | (127,620) | - | (129,479) | 9,510 | (119,969) |
| Balance as of 31 December 2018 | 98 | (1,170) | 60,397 | 1,680,978 | 99,874 | 1,840,177 | 151,642 | 1,991,819 |