Mechanisms of Idelalisib-Associated Diarrhea in Patients With Relapsed Chronic Lymphocytic Leukemia, Indolent Non-hodgkin Lymphoma, or Small Lymphocytic Lymphoma

Inclusion Criteria:

* Food and Drug Administration (FDA)-approved indications for idelalisib of relapsed, histologically confirmed B-cell indolent non-hodgkin lymphoma (iNHL) or chronic lymphocytic leukemia (CLL)
* For iNHL: measureable nodal disease, defined as the presence of \>= 1 nodal lesion that measures \>= 2 cm in a single dimension as assessed by computed tomography (CT) or magnetic resonance imaging (MRI)
* Discontinuation of all other therapies (including radiotherapy or chemotherapy) for the treatment of iNHL \>= 3 weeks before initiation of study treatment
* Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1, or 2
* Absolute neutrophil count \> 750
* Platelets \> 50,000
* Total bilirubin \< 2 X institutional upper limit of normal (ULN)
* Aspartate transaminase (AST) serum glutamic-oxaloacetic transaminase (SGOT)/ alanine transferase (ALT) serum glutamate pyruvate transaminase (SPGT) \< 3 X institutional ULN
* Creatinine \< 2 X institutional ULN
* Women of child-bearing potential and men must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence) prior to study entry, for the duration of study participation, and for 90 days following completion of therapy; should a woman become pregnant or suspect she is pregnant while participating in this study, she should inform her treating physician immediately
* Ability to understand and the willingness to sign a written informed consent; all patients must have signed, witnessed informed consent prior to registration

Exclusion Criteria:

* Prior exposure to idelalisib
* Known histological transformation from iNHL to diffuse large B-cell lymphoma or Richter's Transformation for CLL
* Ongoing treatment with any other investigational agents
* Known central nervous system (CNS) involvement of lymphoma (CNS staging not required)
* History of allergic reactions attributed to compounds of similar chemical or biologic composition to idelalisib
* Uncontrolled inter-current illnesses including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements
* Known human immunodeficiency virus (HIV) infection (HIV testing not required)
* Known John Cunningham (JC) virus infection and/or progressive multifocal leukoencephalopathy (PML)
* Clinically active hepatitis A, B, or C infections
* NOTE: Patients with chronic hepatitis C virus (HCV) or hepatitis B virus (HBV) infection may enroll if other laboratory criteria are met; those with HBV surface antigen positivity may enroll only if maintained on appropriate suppressive antiviral therapy for the duration of enrollment in the trial
* Pregnancy or active nursing of an infant