Liabilities - Performance Obligations (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($)
One Year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Percentage of remaining performance obligation expected to be recognized	76.00%
One year or more
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligations	$ 133.2