Not quite. Consider (note I've trimmed the number of trailing spaces and retained the line ends (but strip them):

use strict;
use warnings;
use Date::EzDate;

my $str = <<DATA;
 Security          : BULGY N V-                         
 Item Overridden   : Earnings Per Share                 
 Initial Value     :  (USD)                             
 Current Value     :  ()                                
 Overridden Value  : 160 (USD)                          
 Effective         : 08/20/1999 through 08/20/2000      
 Override Type     : Data
 SecurityID        : 1076665
 Sedol             : 2451234
 Cusip             : N66696606
 ISIN              : NL0006122988  


DATA

$str =~ s/\n//g;

while ($str =~ /(.*?):\s(.*?)\s\s/g) {
    my ($key, $value) = ($1, $2);
    
    $key =~ s/^\s*//;
    $key =~ s/\s*$//;
    $value =~ s/^\s*//;
    $value =~ s/\s*$//;
    print ">$key: $value<\n";
}
[download]

Prints:

>Security: BULGY N V-<
>Item Overridden: Earnings Per Share<
>Initial Value: (USD)<
>Current Value: ()<
>Overridden Value: 160 (USD)<
>Effective: 08/20/1999 through 08/20/2000<
>Override Type: Data SecurityID<
>: 1076665 Sedol<
>: 2451234 Cusip<
>: N66696606 ISIN<
>: NL0006122988<
[download]

The regex /(\w[\w ]{17}):\s+((?:(?!\w[\w ]{17}:).)*)/g latches on to a 18 character wide label preceeding a : and then grabs characters upto the next label field. The result is:

>Security: BULGY N V-<
>Item Overridden: Earnings Per Share<
>Initial Value: (USD)<
>Current Value: ()<
>Overridden Value: 160 (USD)<
>Effective: 08/20/1999 through 08/20/2000<
>Override Type: Data<
>SecurityID: 1076665<
>Sedol: 2451234<
>Cusip: N66696606<
>ISIN: NL0006122988<
[download]