Revenue - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Disaggregation Of Revenue [Line Items]
Payment terms for customers, lower range		30 days
Payment term for customers, upper range		180 days
Total		$ 38.1
Revenue, Remaining Performance Obligation, Percentage		80.00%
Unearned revenue and customer deposits		$ 50.8		$ 55.9
Reclassified revenue	$ 6.2		$ 19.3
Other Current Liabilities [Member]
Disaggregation Of Revenue [Line Items]
Unearned revenue and customer deposits		1.5		1.4
Other Noncurrent Liabilities [Member]
Disaggregation Of Revenue [Line Items]
Contract liabilities, recognized, noncurrent		$ 27.1		$ 28.0
Minimum [Member]
Disaggregation Of Revenue [Line Items]
Customer contract term		1 year
SEA-US contract term		15 years
Indefeasible right of use of contract term		15 years
Maximum [Member]
Disaggregation Of Revenue [Line Items]
Customer contract term		5 years
SEA-US contract term		25 years
Indefeasible right of use of contract term		25 years
Indefeasible Right of Use, Maximum, in Years		30 years