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v3.21.1

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Self-insured employee benefit costs (Details) | 12 Months Ended
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Dec. 31, 2020 USD ($)
Minimum |
Additional insurance coverage | $ 100,000
Maximum |
Additional insurance coverage | $ 1,000,000

X
- Definition Amount at the high end of insurance coverage. + References No definition available. + Details
Name: | rvp_AdditionalInsuranceCoverage
Namespace Prefix: | rvp_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- 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: |