ASP.NET MVC JsonResult not returning responseText in jQuery.post fail callback function

I am using jQuery $.post to post some data to an ActionResult method inside my controller. When an error is thrown in the controller, it should return the error message within the responseText of the response but it's not working.

The callback function fail seems to be triggered. Just not getting the error message returned. Not sure what I am doing wrong?

This is jQuery posting data:

var postData = ["1","2","3"];

$.post('/MyController/GetSomething', $.param(postData, true))
      .done(function (data) {
              alert('Done!');                        
      })
      .fail(function (xhr, textStatus, errorThrown) {
              alert(xhr.responseText); //xhr.responseText is empty   
      });
 });

Controllers

    public class MyController : BaseController
    {
        public ActionResult GetSomething(List ids)
        {
            try
            {
                GetSomeData(ids);
            }
            catch (Exception ex)
            {
                return ThrowJsonError(new Exception(String.Format("The following error occurred: {0}", ex.ToString())));
            }

            return RedirectToAction("Index");
        }
    }

    public class BaseController : Controller
    {
        public JsonResult ThrowJsonError(Exception ex)
        {
            Response.StatusCode = (int)System.Net.HttpStatusCode.BadRequest;
            Response.StatusDescription = ex.Message;

            return Json(new { Message = ex.Message }, JsonRequestBehavior.AllowGet);
        }
    }