Revenue Recognition - Remaining Performance Obligation (Details)	6 Months Ended
	Jun. 30, 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 performance obligation expected to be recognized in period	62.00%
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 performance obligation expected to be recognized in period	25.00%
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 performance obligation expected to be recognized in period	13.00%