MVC Adding new entry in Master-Detail list collection via PartialView

The objective was to add new entries in the collection via PartialView. In the first entry, checking via debugging it was working fine. But if i add another entry, it doesn't retain or the last entries is not included in the collection. 
What seems to be the problem that my entries are not save/collected in the collection?
Model :

    public class MasterInfo { 
        public int id { get; set; }
        public string name { get; set; }
    }

    public class DetailInfo
    {
        public int id { get; set; }
        public string data_name { get; set; }
        public int data_val { get; set; }
    }

    public class MasterDtlViewModel
    {
        public MasterDtlViewModel() {
            this.Details = new List<DetailInfo>();
        }
        public MasterInfo Master { get; set; }
        public List<DetailInfo> Details { get; set; }
    }

Controller

        public ActionResult NewMaster() 
        {
            var model = new MasterDtlViewModel();
            model.Master = new MasterInfo { id = 1, name = "Chris" };
            model.Details.Add(new DetailInfo
            {
                data_name = "Fee",
                data_val = 1000
            });
            model.Details.Add(new DetailInfo
            {
                data_name = "Charge",
                data_val = 500
            });


            return View("CreateMasterDtlView", model);
        }

        //POST
        public ActionResult NewMaster(MasterDtlViewModel model) 
        {
            var testDetailEntry = model.Details;
            return View("", model);
        }

        //POST
        public ActionResult AddNewEntry(MasterDtlViewModel model, DetailInfo newEntry) 
        {
            model.Details.Add(newEntry);
            return PartialView("_tableDetailView", model);
        }

View :

@model Permit.MasterDtlViewModel

@{

}

<div class="col-md-12">

    @using (Html.BeginForm())
    {
        <div class="panel-group">
            <div class="panel panel-success">
                <div class="panel-heading">
                    <div class="panel-title">Master</div>
                </div>
                <div class="panel-body">
                    <div class="form-group row">
                        @Html.LabelFor(m => m.Master.id, "Customer Id", new { @class = "control-label col-md-4" })
                        <div class="col-md-4">
                            @Html.TextBoxFor(m => m.Master.id, null, new { @class = "form-control" })
                        </div>
                    </div>
                    <div class="form-group row">
                        @Html.LabelFor(m => m.Master.name, "Customer Name", new { @class = "control-label col-md-4" })
                        <div class="col-md-4">
                            @Html.TextBoxFor(m => m.Master.name, null, new { @class = "form-control" })
                        </div>
                    </div>
                </div>
            </div>
        </div>

        <div class="panel-group">
            <div class="panel panel-success">
                <div class="panel-heading">
                    <div class="panel-title">Detail Info</div>
                </div>
                <div class="panel-body">
                    <div class="form-group row">
                        @Html.Label("DataName", "Data Name", new { @class = "control-label col-md-4" })
                        <div class="col-md-4">
                            @Html.TextBox("DataName", null, new { @class = "form-control" })
                        </div>
                    </div>
                    <div class="form-group row">
                        @Html.Label("DataValue", "Data Value", new { @class = "control-label col-md-4" })
                        <div class="col-md-4">
                            @Html.TextBox("DataValue", null, new { @class = "form-control" })
                        </div>
                    </div>

                    <div class="col-md-4 col-md-offset-4">
                        <input type="button" id="AddButton" value="Add" class="btn btn-info" />
                    </div>
                </div>
            </div>
        </div>

        <div class="panel-group">
            <div class="panel panel-success">
                <div class="panel-heading">
                    <div class="panel-title">Added Details</div>
                </div>

                <div id="dtlTable">
                    @Html.Partial("_tableDetailView", Model)
                </div>
            </div>
        </div>

        <div class="col-md-4 col-md-offset-4">
            <input type="submit" value="Save" class="btn btn-success" />
        </div>
    }

</div>

@section scripts {
    <script>
        $("#AddButton").click(function () {
            var mainModel = @Html.Raw(Json.Encode(Model));

            var dataName = $("#DataName").val();
            var dataValue = $("#DataValue").val();

            var inputs = {
                "id": 0,
                "data_name": dataName,
                "data_val": dataValue
            };

            var targetUrl = '/Permit/MastDetail/AddNewEntry';

            $.ajax({
                type: "POST",
                url: targetUrl,
                contentType: "application/json",
                data: JSON.stringify({ model: mainModel, newEntry: inputs  }),
                success: function (result, status, xhr) {
                    $("#dtlTable").html(result).show();
                    $("#DataName").val("");
                    $("#DataValue").val("");
                },
                error: function (xhr, status, error) {
                    // $("#dataDiv").html("Result: " + status + " " + error + " " + xhr.status + " " + xhr.statusText)
                }
            });


        });
    </script>
}

PartialView

@model Permit.MasterDtlViewModel


<div class="panel-body">
    <table class="table table-bordered table-hover table-striped table-responsive">
        <thead>
            <tr>
                <td>Idx</td>
                <td>Data Name</td>
                <td>Value</td>
            </tr>
        </thead>
        <tbody>
            @if (Model.Details != null)
            {
                for (int i = 0; i < Model.Details.Count; i++)
                {
                    <tr>
                        <td><input type="hidden" name="@String.Format("Details[{0}].id",i)" />  @Model.Details[i].id </td>
                        <td><input type="hidden" name="@String.Format("Details[{0}].data_name",i)" />@Model.Details[i].data_name </td>
                        <td><input type="hidden" name="@String.Format("Details[{0}].data_val",i)" />@Model.Details[i].data_val </td>
                    </tr>
                }
            }
        </tbody>
    </table>
</div>

(Note: Having difficulty attaching the codes)