Invalid input syntax for integer

Hello,

I am new to PostgreSQL and have a data format issue that I can't resolve.

The input table from my .csv file (about 10 million records) that I am
importing into PostgreSQL from a different program gives numbers in a format
as follows, for example: 0-1788.000000 to indicate the value -1788.
PostgreSQL gives me the error "invalid input syntax for integer" when I try
to import the number (or invalid for numeric, real, double precision, etc.
when I try to import it in those other formats). When I specify varchar(20)
I get no problems and can import it, but then I can't use it numerically.
How do I either:

- Import the value as NUMERIC or INTEGER or REAL or FLOAT or something
that I can use as a value rather than text, OR
- How do I convert the varchar(20) that I have already imported into a
numeric value?

Thanks

Edwin Winzeler