jQuery Grid Plugin - jqGrid

Here is the column I am trying to add a link for

colModel : [

{name:'ROWNUMBER',index:'ROWNUMBER',hidden:true},

{name:'CAL_MONTH_STR',index:'CAL_MONTH_STR',formatter:'showlink',formatoptions:{baseLinkUrl:'index.cfm',addParam:'&action=report.revenue-detail',idName:'strMth'}}

]

When I do this I end up with a link that looks like this  

index.cfm?strMth=3&action=report.revenue-detail

When in fact I am looking for something like this 

index.cfm?strMth=2009-M12&action=report.revenue-detail

The value for id seems to be coming from the row number and not the actual column data that I am using show link on. Am I doing something wrong? If not is there a way to tell the link what value to use ?