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

Question

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)