v3.8.0.1

Significant Accounting Policies - Additional Information (Detail) - USD ($) |  | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Jul. 31, 2014 | Sep. 30, 2017 | Dec. 31, 2016
Significant Accounting Policies [Line Items] |  |  |
Level III portfolio investments |  | $ 0 | $ 0
Minimum [Member] | Volatility Index Fund [Member] |  |  |
Significant Accounting Policies [Line Items] |  |  |
Percentage of brokerage commissions exceed variable create/redeem fees | 0.02% |  |

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- Definition Level three portfolio investments for significant unobservable inputs fair value. + References No definition available. + Details
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Namespace Prefix: | ck0001415311_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Percentage of brokerage commissions exceed variable create/redeem fees. + References No definition available. + Details
Name: | ck0001415311_PercentageOfBrokerageCommissionsExceedVariableCreateOrRedeemFees
Namespace Prefix: | ck0001415311_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Significant accounting policies. + References No definition available. + Details
Name: | ck0001415311_SignificantAccountingPoliciesLineItems
Namespace Prefix: | ck0001415311_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=ck0001415311_VolatilityIndexFundMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |