Clients and other receivable (Details) - USD ($) $ in Thousands |
Dec. 31, 2017 |
Dec. 31, 2016 |
|---|---|---|
| Clients and other receivables [Abstract] | ||
| Trade receivables | $ 186,728 | $ 151,199 |
| Tax receivables | 39,607 | 29,705 |
| Prepayments | 6,375 | 10,261 |
| Other accounts receivable | 11,739 | 16,456 |
| Clients and other receivables | 244,449 | 207,621 |
| Up to 3 Months [Member] | ||
| Clients and other receivables [Abstract] | ||
| Trade receivables | 186,728 | 151,199 |
| Euros [Member] | ||
| Clients and other receivables [Abstract] | ||
| Trade receivables | 109,165 | 98,798 |
| Rand [Member] | ||
| Clients and other receivables [Abstract] | ||
| Trade receivables | 23,792 | 12,807 |
| Other [Member] | ||
| Clients and other receivables [Abstract] | ||
| Trade receivables | 7,363 | 7,151 |
| All Foreign Currencies [Member] | ||
| Clients and other receivables [Abstract] | ||
| Trade receivables | $ 140,320 | $ 118,756 |