Subsequent events Subsequent Events (Details) - Subsequent Event $ in Millions	Mar. 05, 2019 USD ($) agreement	Feb. 01, 2019 director
Subsequent Event [Line Items]
Number of Directors | director		7
Number of agreements related to the sale | agreement	2
February 2019 Sale
Subsequent Event [Line Items]
Consideration received from transfer of ownership	$ 5
December 2018 Sale
Subsequent Event [Line Items]
Consideration received from transfer of ownership	$ 2