how do I create running quarter and year to date totals in months where there is no detail activity

 I am using this partition statement which works great as long as there are source records for the fields specified for each month.When there are not all source records in a subsequent month then this does not create a value which returns in correct summarization

If I have a January amount of $100 for D_DISTREP_SKEY  but in February then there isn t a record i want the $100 from the prior month to also show in February which is not happening.

What do I need to add to this to make the prior month amounts carry forward even when there is no current month activity ?