Unless we're talking about a nuclear detonation in low earth orbit, which is clearly beyond the means of any forseeable terrorist organization, EMP effects will be localized and shouldn't be a problem outside the immediate area of the blast. Financial institutions maintain (or at least are supposed to maintain) offsite archives and should be able to reconstruct their data. But it may take a very long time to get access to your money.
I would be more worried about secondary economic effects. A nuclear attack on NYC, for example, would have a chain reaction effect and could lead to a nationwide, and perhaps worldwide, depression.
If a modest sized nuke was exploded off shore (on a ship, not a air blast) from one of our ports like NYC. How far away would the EMP effects travel?