A den of thieves
The outer court was meant for "all nations", meaning foreigners and Gentiles. When Jesus say's "you have made it a den of thieves"; no one of this day has described that the Sadducees took (stolen) this outer court away from the Gentiles. They have stolen it for their own purposes, to make money. The Gentiles were pushed out and not allowed to pray in "the house of prayer". This is the primary reason Jesus said basically you are all thieves if you are here!