Linux – Per-process CPU/MEM utilization

If you're using Bash, you can run disown -h job

disown

disown [-ar] [-h] [jobspec ...]

Without options, each jobspec is removed from the table of active jobs. If the -h option is given, the job is not removed from the table, but is marked so that SIGHUP is not sent to the job if the shell receives a SIGHUP. If jobspec is not present, and neither the -a nor -r option is supplied, the current job is used. If no jobspec is supplied, the -a option means to remove or mark all jobs; the -r option without a jobspec argument restricts operation to running jobs.

99% cpu usage means almost total utilization of single core.

if your system is totally loaded [ couple threads each hogging one cpu ] - you'll see 400% usage on quad core or 800% usage on two quad cores.

processes/threads are re-assigned between cpus - that's why you see 25% of utilisation on each of cores. but you can set affinity for them.. then they'll stick to selected processors/cores.