I expect that the following extract will fail, as the max size of INT is 2,147,483,647 (10 Digits).
Even converting to BIGINT MAY fail, depending on the actual data, as the max size of BIGINT is 9,223,372,036,854,775,807 (19 Digits)
CONVERT([INT], SUBSTRING([ID_NUM], (3), (20)), (0))
Then when adding it to 111210000000. are you attempting to do a string concatenation, or are you trying to do addition