Accounting policies (Intangible assets) (Details) |
12 Months Ended |
|---|---|
Dec. 31, 2017 | |
| Proprietary technology [Member] | |
| Finite-Lived Intangible Asset, Useful Life | 20 years |
| Backlog [Member] | |
| Finite-Lived Intangible Asset, Useful Life | 1 year |
| Virtual Reality Technologies [Member] | |
| Finite-Lived Intangible Asset, Useful Life | 10 years |