$(document).ready(function(){
	if ($('#shipthis').attr('checked')) {
		$('.shipping_field').removeAttr('disabled');
	} else {
		$('.shipping_field').attr('disabled',true);
	}
	
	$('body').click(function(event) {
		if ($(event.target).is('#shipthis')) {
			if ($('#shipthis').attr('checked')) {
				$('.shipping_field').removeAttr('disabled');
			} else {
				$('.shipping_field').attr('disabled',true);
			}
		}
	}); // body.click
	
	

}); // document.ready