Can someone explain to me why this emberjs observeable doesn't get fired?

Whenever I save data ( self.get('content').pushObject(record);) and push the record back into the content Array, the observable doesn't get fired. I need the observable to fire so the content array gets sorted again. Can you please explain to me why its not firing?

saveIdea.IndexController = Ember.ArrayController.extend({
    appName: 'My First Example',
    todaysDayOfMonth: moment().format('DD'),
    todaysMonth: moment().format('MMMM'),
    body: '',
    taggy: '',
    content : Em.A(),
    sortContent : function()
    {
        var ideas = this.get('content').toArray();
        ideas.sort(function(a, b) {
            if (moment(b.get('date')).isBefore(moment(a.get('date')))) {
                return -1
            } else {
                return 1
            }
        });
        this.set('content',ideas)
    },
    todaysIdeas: function(){
            this.sortContent();
    }.observes('content.[]'),
    actions: {

        save: function() {

            var self = this;

            var idea = this.store.createRecord('idea', {
                body: this.get('body'),
                tag: this.get('taggy')
            });
            idea.save().then(function(record) {
                self.get('content').pushObject(record);
            });
        }
    }
});