Revenue from Contracts with Customers - Contract Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Costs of Obtaining Contracts with Customers
Contract liability, Beginning of period	$ 3.9
Impact of change in accounting policy		$ 2.1
Deferral	16.1	17.5
Revenue recognized	(15.8)	(15.7)
Contract liability, End of period	4.2	3.9
Current portion of contract liabilities			$ 3.6	$ 3.3
Non-current portion of contract liabilities			0.6	0.6
Total contract liabilities	$ 4.2	$ 3.9	$ 4.2	$ 3.9
Residential Subscription
Costs of Obtaining Contracts with Customers
Contract liability, term of contract	5 months
Business Subscription
Costs of Obtaining Contracts with Customers
Contract liability, term of contract	30 months