Description of Business and Significant Accounting Policies - Nature of Operations (Details)	12 Months Ended
	Dec. 31, 2017 segment
Schedule of Accounting Policies [Line Items]
Service agreement term	1 year
Number of reportable segments	2
Minimum
Schedule of Accounting Policies [Line Items]
Days to notify cancellation of service	30 days
Initial period of service term	60 days
Maximum
Schedule of Accounting Policies [Line Items]
Days to notify cancellation of service	90 days
Initial period of service term	120 days