Revenue - Performance Obligations (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($)
Revenue
Future revenue related to current unsatisfied performance obligations	$ 22,505
Revenue, Practical Expedient, Remaining Performance Obligation [true/false]	true
Revenue, Practical Expedient, Incremental Cost of Obtaining Contract [true/false]	true
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-01-01
Revenue
Future revenue related to current unsatisfied performance obligations	$ 1,825
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue
Future revenue related to current unsatisfied performance obligations	$ 6,898
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue
Future revenue related to current unsatisfied performance obligations	$ 4,509
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue
Future revenue related to current unsatisfied performance obligations	$ 9,273
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	12 months