EtherDelta, ForkDelta and IDEX crypto exchanges are decentralized, meaning, no one can manilupate the exchange walls but somehow they're not that reliable unlike big crypto exchanges like Binance, HitBTC, Poloneix, GDAX etc.
recently EtherDelta was attacked and accounts were stolen and so as big crypto exchanges but the users on popular exchanges will be refunded in case the coins lost unlike decentralized exchanges mentioned above.