Revenue from Contracts with Customers - Performance Obligations, Expected Timing of Recognition, Narrative (Details)	9 Months Ended
	Sep. 30, 2018
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligation, percentage of revenue	6.00%
Performance obligation, period for recognition	3 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligation, percentage of revenue	22.00%
Performance obligation, period for recognition	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligation, percentage of revenue	72.00%
Performance obligation, period for recognition	14 years 7 months 6 days