Martijn I am looking for an obscure detective series and came across a Huffington Post collection of "Television's Most Memorable Male Detectives of All Time". Which is definitely U.S. oriented. It forgets Hercule Poirot (played by David Suchet for over 20 years) and Tom Barnaby (played by John Nettles for over 10 years). It does include Sherlock Holmes, though I do not know a single long running TV potrayal of Holmes.

Nkrs Both Midsomer Murders and Hercule Poirot are personal favorites. I found the article you mention (or at least I think I did), no mention of Jessica Fletcher. Maybe Elementary could be a fit for the long running Sherlock Holmes - word is out that there will be a fifth season.

Martijn I hadn't looked at the list of female detectives yet. But you are right, no Jessica Fletcher. And if you are really "all time" I feel like female detectives should also include Laura Holt from Remington Steele. HuffPo is letting us detective buffs down.