Revenue from Contracts with Customers - Costs of Obtaining Contracts (Details) $ in Millions	Sep. 30, 2018 USD ($)
Prepaid expenses and other
Costs of Obtaining Contracts with Customers
Current portion of costs of obtaining contracts with customers	$ 5.0
Other noncurrent assets
Costs of Obtaining Contracts with Customers
Non-current portion of costs of obtaining contracts with customers	$ 18.1
Residential Subscription \| Minimum
Costs of Obtaining Contracts with Customers
Costs of contracts with customers, amortization period	3 years
Residential Subscription \| Maximum
Costs of Obtaining Contracts with Customers
Costs of contracts with customers, amortization period	4 years
Business Subscription \| Minimum
Costs of Obtaining Contracts with Customers
Costs of contracts with customers, amortization period	6 years
Business Subscription \| Maximum
Costs of Obtaining Contracts with Customers
Costs of contracts with customers, amortization period	7 years

Amortization period of cost capitalized in obtaining or fulfilling contract with customer, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 340
-SubTopic 40
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=68051541&loc=SL49131251-203054

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+ References

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- Definition

Amount, after accumulated amortization and accumulated impairment loss, of asset recognized from cost incurred to obtain or fulfill contract with customer; classified as current.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 340
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=68051541&loc=SL49131252-203054

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Amount, after accumulated amortization and accumulated impairment loss, of asset recognized from cost incurred to obtain or fulfill contract with customer; classified as noncurrent.

+ References

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