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Summary of Significant Accounting Policies - Significant Estimates Used by Management in Determining Fair Values of Customer Relationships Acquired (Detail) | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2018 | Dec. 31, 2017
Minimum |  |
Indefinite-lived Intangible Assets [Line Items] |  |
Discount rates | 20.00% | 17.00%
Customer attrition rates | 20.00% | 15.00%
Maximum |  |
Indefinite-lived Intangible Assets [Line Items] |  |
Discount rates | 27.00% | 25.00%
Customer attrition rates | 33.00% | 78.00%

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- Definition Fair Value Inputs, Customer Attrition Rates + References No definition available. + Details
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- Definition Fair Value Inputs, Rate Of Return + References No definition available. + Details
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- Definition 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. + References No definition available. + Details
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- Details
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