v3.21.1

Offering Costs - Additional Information (Detail) | 3 Months Ended
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Mar. 31, 2021
Investment Holdings [Line Items] |
Offering costs, amortization period | 12 months

X
- Definition Offering costs, amortization period, months. + References No definition available. + Details
Name: | ck0001415311_OfferingCostsAmortizationPeriod
Namespace Prefix: | ck0001415311_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- 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
Name: | us-gaap_InvestmentHoldingsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration