Revenue from Contracts with Customers - Performance Obligations, Expected Timing of Recognition, Narrative (Details)	3 Months Ended
	Mar. 31, 2018
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligation, percentage of revenue	17.00%
Performance obligation, period for recognition	9 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	19.00%
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	64.00%
Performance obligation, period for recognition	7 years 6 months