Laravel 5 One To Many Relation Form Model Binding

I'm using Laravel the first time and am working on an application with which I can generate invoices. Each invoice can have multiple positions. This means there is a one to many relation.

When creating a new invoice there are the inputs for the first position and via ajax the inputs to add more positions can be added. I use an array for the positions and make a random index.

<?php $c = rand(); ?>

{!! Form::text('position['.$c.'][title]', null, ['class' => 'form-control']) !!}
{!! Form::textarea('position['.$c.'][description]', null, ['class' => 'form-control']) !!}

This works perfectly fine so far.

Now when it comes to editing an invoice the problem arises. What do I have to do to get the Form-Model Binding working?

Now I check how many positions I have and load the snippet with the position inputs that often and pass in the data.

@foreach( $document->positions as $position)
    @include('documents._position', [$position])
@endforeach

But the values don't appear in the input fields. What do I have to do to get this working?

And a second thing would be how can I sync the positions? I now just delete the existing ones after editing an invoice and make new ones. Is there a better way to do this?