Revenue - Performance Obligation (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($)
Revenue
Total	$ 139,563
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-04-01
Revenue
Total	$ 50,856
Performance obligation
Unsatisfied performance obligation, period	6 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue
Total	$ 47,385
Performance obligation
Unsatisfied performance obligation, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue
Total	$ 18,616
Performance obligation
Unsatisfied performance obligation, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue
Total	$ 9,205
Performance obligation
Unsatisfied performance obligation, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue
Total	$ 5,123
Performance obligation
Unsatisfied performance obligation, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue
Total	$ 8,378
Performance obligation
Unsatisfied performance obligation, period