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v3.21.2

Commitments and Contingencies - Additional Information (Detail) | 9 Months Ended
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Sep. 30, 2021
Minimum [Member] |
Commitments And Contingencies [Line Items] |
Number of months of salary paid as severance | 3 months
Maximum [Member] |
Commitments And Contingencies [Line Items] |
Number of months of salary paid as severance | 24 months

X
- Definition Commitments and contingencies. + References No definition available. + Details
Name: | nsit_CommitmentsAndContingenciesLineItems
Namespace Prefix: | nsit_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The number of months of salary that would be payable to certain officers and management teammates, if severance payments under current employment agreements or plan payments were to become payable. + References No definition available. + Details
Name: | nsit_NumberOfMonthOfSalaryPaidAsSeveranceOnChangeOfControl
Namespace Prefix: | nsit_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |