Revenue - Nature of goods and services (Details) - USD ($) $ in Millions	1 Months Ended	204 Months Ended
	May 31, 2019	Dec. 31, 2035	Dec. 31, 2019	Dec. 31, 2018
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Deferred revenue transferred to buyer during sale	$ 22.0
Contract with Customer, Liability			$ 9.2	$ 33.4
Minimum | Scenario, Forecast [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Recognition of Deferred Revenue, Expected Annual Amount		$ 0.2
Maximum | Scenario, Forecast [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Recognition of Deferred Revenue, Expected Annual Amount		$ 1.0