Subsequent events (Details) - Subsequent Event [Member] - USD ($) $ in Millions	12 Months Ended	24 Months Ended
	Dec. 31, 2017	Dec. 31, 2018
Subsequent Event [Line Items]
Launchpad phase 1 pretax savings	$ 20.0	$ 45.0
Launchpad Phase 2 pretax savings	30.0
Launchpad Phase 2 pretax savings - severance	14.0
Launchpad Phase 2 pretax savings - facility	$ 16.0