In Laravel, how do I retrieve a random user_id from the Users table for Model Factory seeding data generation?

Currently, in my ModelFactory.php, I have:

$factory->define(App\Reply::class, function (Faker\Generator $faker) {
  return [
    'thread_id' => 1,
    'user_id' => 1,
    'body' => $faker->paragraph
  ];
});

I would like to generate a random user_id from one of the user ID's already stored in the user table. I'm stumped because I don't know the way to display data output to code properly, and I was wondering how I would be able to allow Laravel to choose a random user ID and insert into the database. Thank you! :)

via Simon Suh