Fatal error when not numeric value - PostgreSQL 9.2

Hi all,

Below is an example of the auto-generated update query, with client-supplied keys (_iid). There's a fatal error when _iid is not numeric. However; this should accept any value.

Question: How could I do something that would allow _iid to be more than just an INT?

WITH
    in_rows AS (
      SELECT
        CAST(customer_id AS BIGINT),
        csv_data,
        freshbooks_id,
        myob_id,
        ppy_id,
        qb_id,
        xero_id,
        _iid
      FROM
        (
          VALUES
('3905', E'\x1A', E'\x1A', 'c59894c-142b6', E'\x1A', E'\x1A', E'\x1A', '44'),
('39107', E'\x1A', E'\x1A', '6260-2ba1', E'\x1A', E'\x1A', E'\x1A', '65e-0f0d-49b4-9ac1-a8752ba1'),