A modified Symfony Forms "timezone" type that also displays the timezone offset

TimezoneType.php

<?php
/**
 * A modified version of the original symfony form type that adds the timezone offset.
 * 
 * Original version at:
 * https://github.com/symfony/symfony/blob/2.7/src/Symfony/Component/Form/Extension/Core/Type/TimezoneType.php
 */

/*
 * Installation:
 * =============
 * # services.yml
 * services:
 *     # ...
 *     acme.form.timezone:
 *       class: Acme\AcmeBundle\Form\Extension\TimezoneType
 *       tags:
 *         - { name: form.type, alias: acme.form.timezone }
 * 
 * Usage:
 * ======
 * $builder
 *     ->add("timezone", "acme.form.timezone")
 *     // ...
 */

namespace Acme\AcmeBundle\Form\Extension;

use Symfony\Component\Form\AbstractType;
use Symfony\Component\OptionsResolver\OptionsResolver;

class TimezoneType extends AbstractType
{
    /**
     * Stores the available timezone choices
     * @var array
     */
    private static $timezones;

    /**
     * {@inheritdoc}
     */
    public function configureOptions(OptionsResolver $resolver)
    {
        $resolver->setDefaults(array(
            "choices" => self::getTimezones(),
            "choices_as_values" => true
        ));
    }

    /**
     * {@inheritdoc}
     */
    public function getParent()
    {
        return "choice";
    }

    /**
     * {@inheritdoc}
     */
    public function getName()
    {
        return "acme.form.timezone";
    }

    /**
     * Returns the timezone choices.
     *
     * The choices are generated from the ICU function
     * \DateTimeZone::listIdentifiers(). They are cached during a single request,
     * so multiple timezone fields on the same page don"t lead to unnecessary
     * overhead.
     *
     * @return array The timezone choices
     */
    public static function getTimezones()
    {
        if (null === static::$timezones) {
            static::$timezones = array();

            foreach (\DateTimeZone::listIdentifiers() as $timezone) {
                $parts = \explode("/", $timezone);
                
                $dateTimeZone = new \DateTimeZone($timezone);
                $dateTime = new \DateTime("now", $dateTimeZone);
                $offset = "GMT " . $dateTime->format("P");

                if (\count($parts) > 1) {
                    $name = \sprintf("%s (%s)", $timezone, $offset);
                } else {
                    $name = \sprintf("%s (%s)", "Other", $offset);
                }

                static::$timezones[\str_replace("_", " ", $name)] = $timezone;
            }
        }

        return static::$timezones;
    }
}