Note 5 - Asset Retirement Obligation (Details Textual)	3 Months Ended
Mar. 31, 2019
Current Year Inflation Rate	4.08%
Change In Present Value, Percent	3.25%

The percentage by which the liability is increased annually for the change in its present value.

No definition available.

Name:	rsrv_ChangeInPresentValuePercent
Namespace Prefix:	rsrv_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration