Revenue from Contracts with Customers - Performance Obligations, Expected Timing of Recognition, Narrative (Details)	6 Months Ended
	Jun. 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	12.00%
Performance obligation, period for recognition	6 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	21.00%
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	67.00%
Performance obligation, period for recognition	7 years 10 months 24 days