Revenue (Assets Recognized from the Costs to Obtain a Contract with a Customer) (Details)	3 Months Ended
Mar. 31, 2018
Minimum
Capitalized Contract Cost [Line Items]
Amortization period	2 years
Maximum
Capitalized Contract Cost [Line Items]
Amortization period	5 years

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_CapitalizedContractCostLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration