Revenue from Contracts with Customers - Performance Obligations Unsatisfied at End of Period (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Estimated remaining performance period	3 months
Performance obligation unsatisfied or partially unsatisfied	$ 92
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Estimated remaining performance period	1 year
Performance obligation unsatisfied or partially unsatisfied	$ 369
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Estimated remaining performance period	1 year
Performance obligation unsatisfied or partially unsatisfied	$ 369
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Estimated remaining performance period	1 year
Performance obligation unsatisfied or partially unsatisfied	$ 303
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Estimated remaining performance period	1 year
Performance obligation unsatisfied or partially unsatisfied	$ 153
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Estimated remaining performance period	1 year
Performance obligation unsatisfied or partially unsatisfied	$ 1,429