v3.8.0.1
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