What Javascript regex pattern can be used to capture text in potentially nested parentheses?

I have a string that can look like either of these Adjuster, Carrier 3 (Carrier 3) or Adjuster, Carrier 3 (Carrier 3 (Test))

I want to capture the contents within the first set of parentheses. My original regex pattern was \((.+?)\) (non-greedy), so I can capture the text as group #1.

var selectedOwnerText = /* GET THE TEXT FROM NODE/FIELD/ETC. */, 
    carrierName = '',
    rePattern = /\((.+?)\)/;

    if (selectedOwnerText != '') {
       carrierName = selectedOwnerText.match(rePattern);
       if (carrierName != null) {
          carrierName = carrierName[1];
       }
    }
 // Rest of code...

This works in the first text case, but in the second text case it grabs the outer parentheses e.g. (Carrier 3 (Test).

Is there a regex pattern that can capture the text inside the outer parentheses, which may include parentheses as well? I want either Carrier 3 or Carrier 3 (Test) extracted from the above.

EDIT: I have just been told that this data field is free-form text, so anything could appear inside the outer parentheses. So, I would need to capture everything inside the outer parentheses.

EDIT 2: I gave one user the correct answer, because it answered the original question (assuming only one set of inner parentheses). Now that I know the text could be anything, a Javascript regex pattern is impossible, and I abandoned the regex approach. I dived into the server-side code and surfaced a JSON literal of the data I needed, so as the page/Javascript is being created, I can use the data structure to get the content I need without worrying about what the string actually looks like. Thanks to all who tried to help!