Revenue from Contracts with Customers - Narrative (Details)	12 Months Ended
	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Contract terms	Generally, contracts are billed in arrears on a quarterly basis and have a three year duration, after which the customer can terminate the agreement with a three to twelve month notice.
Disaggregation of Revenue [Line Items]
Termination period	60 days
Minimum
Disaggregation of Revenue [Line Items]
Termination period	3 months
Maximum
Disaggregation of Revenue [Line Items]
Termination period	12 months