Flat ideals and stability in integral domains

We introduce the concept of quasi-stable ideal in an integral domain D (a nonzero fractional ideal I of D is quasi-stable if it is flat in its endomorphism ring (I:I)) and study properties of domains in which each nonzero fractional ideal is quasi-stable. We investigate some questions about flatness that were raised by S. Glaz and W.V. Vasconcelos in their 1977 paper [17].