Revenue from Contracts with Customers - Services Length (Details)	6 Months Ended
	Jun. 30, 2018
Business Subscription
Revenue from Contracts with Customers
Subscription services, contract term	30 months
Minimum | Residential Subscription
Revenue from Contracts with Customers
Subscription services, contract term	12 months
Maximum | Residential Subscription
Revenue from Contracts with Customers
Subscription services, contract term	24 months