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Summary of Significant Accounting Policies - Stock-Based Compensation (Detail) | 12 Months Ended
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Dec. 31, 2017 shares
Restricted Stock Units to be Settled in Cash |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Number of common stock shares that may be received by RSU holder (in shares) | 1

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- Definition Amount in cash received for each RSU is equal to the fair value of this number of Quanta common stock shares. + References No definition available. + Details
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Balance Type: | na
Period Type: | duration

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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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Balance Type: | na
Period Type: | duration

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- Details
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Data Type: | na
Balance Type: |
Period Type: |