Revenue Recognition - Performance Obligations (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 (as a percent)	33.00%
Expected timing of satisfaction period	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 (as a percent)	33.00%
Expected timing of satisfaction period	12 months