Revenue - Method of Adoption (Details) - USD ($)	3 Months Ended
Mar. 31, 2017	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2016
Revenue from Contract with Customer [Abstract]
Adjustment to revenue and cost of services and products for adoption of ASC 606	$ 28,600,000
Capitalized Contract Cost, Net, Incremental Assets Related to Fulfillment and Acquisition Costs			$ 32,300,000
Capitalized Contract Cost, Net		$ 32,400,000.0	$ 32,400,000.0	$ 32,000,000.0	$ 30,600,000.0

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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

Name:	us-gaap_CapitalizedContractCostNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant