This research trial studies the mechanisms of idelalisib-associated diarrhea in patients with chronic lymphocytic leukemia, indolent non-hodgkin lymphoma, or small lymphocytic lymphoma that has come back after a period of improvement. The cancer treatment drug idelalisib triggers diarrhea in some patients. Studying stool, blood, and tissue samples in the lab from patients who are given idelalisib may help doctors learn more about the side effects and may help to treat them in future patients.