Revenue Recognition - Remaining Performance Obligation (Details)	3 Months Ended
	Mar. 31, 2018
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-01-01
Remaining performance obligations
Revenue, Remaining performance obligation, expected timing of satisfaction period	12 months
Percentage of remaining perfromance obligation expected to be recognized in period	58.00%
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Remaining performance obligations
Revenue, Remaining performance obligation, expected timing of satisfaction period	12 months
Percentage of remaining perfromance obligation expected to be recognized in period	26.00%
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Remaining performance obligations
Revenue, Remaining performance obligation, expected timing of satisfaction period	12 months
Percentage of remaining perfromance obligation expected to be recognized in period	16.00%