The code below uses txtbox as the name of the text box the user enters the Idle value, and HideTxtbox as the name of the text box to be hidden. Note that I set an else statement, this is used to ensure that if the user entered Idle on the text box and the field is was hidden that it displays back, otherwise once it is hidden it remains hidden regardless of what values are entered on the text box. The user only has to enter Idle 1 time to make the button hide, after that the button is hidden until something else makes it visible, the ELSE statement prevents this from happening.
Sub txtbox_AfterUpdate()
If me.txtbox.value = "Idle" Then
me.HideTxtbox.visible = False
Else
me.HideTxtbox.Visible = True
End If
End Sub