v3.8.0.1

Risk - Additional Information (Detail) | 9 Months Ended
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Sep. 30, 2017
Unusual Risk or Uncertainty [Line Items] |
Percentage of calculation on simple inverse correlation | 200.00%
Forward Agreements [Member] |
Unusual Risk or Uncertainty [Line Items] |
Exposure to swap agreements or forward contracts | 100.00%
Ultrashort Fund [Member] |
Unusual Risk or Uncertainty [Line Items] |
Leverage risk benchmark | 50% at any point in the day

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- Definition Percentage of calculation on simple inverse correlation. + References No definition available. + Details
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Namespace Prefix: | ck0001415311_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Percentage of credit exposure. + References No definition available. + Details
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Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Risk related to changes in benchmark interest rate. + References No definition available. + Details
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Namespace Prefix: | ck0001415311_
Data Type: | xbrli:stringItemType
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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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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
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Period Type: | duration

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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |

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