Revenues - Performance Obligation (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Products and Services
Disaggregation of Revenue [Line Items]
Revenue recognized, percent	93.50%	93.50%	92.20%
Product
Disaggregation of Revenue [Line Items]
Revenue recognized, percent	6.50%	6.50%	7.80%