Teradata SQL Regular Expression to compare date format

Verify if date is in format dd-MMM-yyyy

select
 regexp_similar(a_date,'^(([0-9])|([0-2][0-9])|([3][0-1]))\-(JAN|FEB|MAR|APR|MAY|JUN|JUL|AUG|SEP|OCT|NOV|DEC)\-\d{4}$') = 1
from table1