Contract Assets and Contract Liabilities (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Deferred Costs [Abstract]
Contract assets	$ 2.8	$ 2.5	$ 2.8
Contract Liabilities [Abstract]
Contract liabilities, current		6.8	1.1
Contract liabilities	1.6	7.0	1.6
Movement in Deferred costs [Rollforward]
Beginning balance	2.8
Plus: contractual additions	3.7
Less: amortization	4.0
Ending deferred mobilization and upgrade/modification costs	2.5
Movement in Deferred Revenue [Roll Forward]
Beginning balance	1.6
Plus: contractual additions	10.0
Less: amortization	4.6
Ending deferred mobilization and upgrade/modification revenue	$ 7.0
Deferred Revenue [Member]
Contract Liabilities [Abstract]
Contract liabilities, current		6.8	1.1
Prepaid Expenses and Other Current Assets [Member]
Deferred Costs [Abstract]
Contract assets, current		2.4	2.8
Other Noncurrent Liabilities [Member]
Contract Liabilities [Abstract]
Contract liabilities, noncurrent		0.2	0.5
Other Assets [Member]
Deferred Costs [Abstract]
Contract assets, non-current		$ 0.1	$ 0.0