How to get formId from leadgen webhook on facebook?

Question

I created a webhook to track leads on my facebook page. I need formId of lead, but my logs are shown below.

[field] => leadgen
      [value] => stdClass Object
            (
              [ad_id] => 0
              [form_id] => 2.6147643765585E+14
              [leadgen_id] => 2.6356365078047E+14
              [created_time] => 1491489109
              [page_id] => 4.3192338381483E+14
              [adgroup_id] => 0
            )

[form_id] is shown as 2.6147643765585E + 14, but the actual formId is different. I think it is encoded correctly?

How to get formId in decoded form, I mean the original form, for example

 "field" => "leadgen",
      "value" => array(
        "leadgen_id" => 123123123123,
        "page_id" => 123123123,
        "form_id" => 12312312312,
        "adgroup_id" => 12312312312,
        "ad_id" => 12312312312,
        "created_time" => 1440120384
      )

Thanks in advance.