Datepicker is shown behind the modal bootstrap

I have a bootstrap modal:

<!-- Modal content-->
<div class="modal-content">
  <div class="modal-header">
    <button type="button" class="close" data-dismiss="modal">&times;</button>
    <h4 class="modal-title">Agendar reunião do evento <?php echo $row- >denominacao; ?></h4>
  </div>
  <div class="modal-body">
    <div class="box">
      <div class="box-body">
        <?php echo form_open('utilizador/alterarAgendamento'); ?>
          <div class="row">
            <div class="form-group col-xs-6">
              <label>Data</label>
              <div class="input-group">
                <div class="input-group-addon">
                  <i class="fa fa-calendar"></i>
                </div>
                <input type="hidden" value="<?php echo $row->idevento; ?>" name="idevento" />
                <input type="text" class="form-control data_inserir" readonly="readonly" name="data" />
              </div>
            </div>
            <div class="form-group col-xs-6 bootstrap-timepicker">
              <label>Hora</label>
              <div class="input-group">
                <input type="text" class="form-control timepicker" name="hora" />
                <div class="input-group-addon">
                  <i class="fa fa-clock-o"></i>
                </div>
              </div>
            </div>
          </div>
          <div class="row">
            <div class="form-group col-xs-12">
              <label>Notas</label>
              <textarea class="form-control" rows="3" name="nota" placeholder=""> </textarea>
            </div>
          </div>
          <button type="submit" class="form-control">Re-Agendar</button>
          <?php echo form_close(); ?>
      </div>
    </div>
  </div>
</div>

The input with class data_inserir is calling the dataPicker function, but this appears behind the modal and I can not get it to stay ahead.