Laravel 5 - List database entries where

I am trying to list all entries which fall under a where condition. If I do the following, I get all the entries returned

$users = User::lists('userName', 'id');

However, I am looking to return only the users who have a department id of 3. So I am doing

$users = User::lists('userName', 'id')->where('departmentId', 3);

However, this returns an empty result set. In my database, I do have users with this department id.

How can I get the lists statement working?

Just a note, the following returns the result I need

$users = User::select('userName', 'id')->where('departmentId', 3)->get();

However, in my edit form, because I have this

!! Form::select('csManager', $users, Input::old('users'), ['class' => 'csManager']) !!}

The old input is not selected and the data is showing up as an array. I know the way to fix this is to do my select like this

<select class="csManager" name="csManager">
    @foreach($users as $user)
    <option value="{{ $user->id }}">{{ $user->userName }}</option>
    @endforeach
</select>

But then I am not sure how to display the old user within the above select.

Any help appreciated.

Thanks

via Chebli Mohamed