[A protester waves a Greek flag during a demonstration outside the parliament building in central Athens]By Jan Strupczewski and Francesco Guarascio BRUSSELS (Reuters) - Euro zone governments on Wednesday offered Greece debt relief in 2018, but left key details for later in a bid to bridge Germany's view that no immediate action was needed and the International Monetary Fund's call for decisions now. The late-night compromise spared the battered European Union the risk of another Greek crisis this year, less than 12 months after Athens was on the brink of ejection from the currency area by rejecting austerity measures and defaulting on an IMF loan.