One ViewModel for UserControl and Window or separate ViewModels

I have MainWindow and AddEdit UserControl. Inside MainWindow I render this AddEdit like <Views:AddEditData />, previous this namespace is added to Window element:

xmlns:Views="clr-namespace:MyProject.WPF.Views"

+++++++++++++++ ++++++++++++++++
ListOfData    + + DataDetails  +
              + +              +
   DataOne    + + Name: txtBox1+
   DataTwo    + +              +
   DataThree  + +              +
              + +  Save data   +
+++++++++++++++ ++++++++++++++++

When user selects data on left side (DataTwo for example) I want to display it's properties (for simplicity only Name property) inside AddEdit user control (DataDetails panel).

Since this UserControl is stored separately from the MainWindow should I use same MainWindowViewModel and same datacontext or should I create separated ViewModel for AddEdit UserControl?

Hopefully this sounds clear, if not please ask for details.