Get Only Numbers from a String in PLSQL

Example 1:

SELECT  REGEXP_REPLACE(TRIM(REGEXP_SUBSTR('print document 2000, document 1000', '[^,]+', 1, LEVEL)), '[^[:digit:]]', '') str
FROM    DUAL
CONNECT BY INSTR('print document 2000, document 1000', ',', 1, LEVEL - 1) > 0;

Example 2:

SELECT REGEXP_REPLACE('print document 2000, document 1000', '[^[:digit:]]', '') FROM DUAL;