How long is cocaine detectable in the system?

It depends what you mean by "detectable" and "the system". It depends on your metabolism, if you have been hydrating yourself adequately etc but generally speaking most urine and oral fluid tests are able to detect Benzoylecgonine (This is, the metabolite of cocaine) for up to and including 4 days. (This applies to blood samples too).

Hair strand tests (which are more expensive and take longer to process) can detect back as far as it when it was last cut - sometimes up to 2 years.