Key Inclusion Criteria:

1. Histologically confirmed diagnosis of B-cell follicular lymphoma
2. ≥2 prior systemic treatments for follicular lymphoma.
3. Previously received an anti-CD20 antibody and an appropriate alkylator-based combination therapy.
4. Disease progression after completion of most recent therapy or refractory disease.
5. Presence of measurable disease.
6. Availability of archival tissue confirming diagnosis.
7. Eastern Cooperative Oncology Group (ECOG) performance status of 0,1 or 2.
8. Adequate renal and hepatic function.

Key Exclusion Criteria:

1. Prior exposure to a Bruton's tyrosine kinase (BTK) inhibitor.
2. Known central nervous system involvement by leukemia or lymphoma.
3. Evidence of transformation from follicular lymphoma to other aggressive histology.
4. Allogeneic hematopoietic stem cell transplantation within 12 months of enrollment
5. Prior malignancy within the past 2 years, except for curatively treated basal or squamous cell skin cancer, superficial bladder cancer, carcinoma in situ of the cervix of breast, or localized Gleason score 6 prostate cancer.
6. Clinically significant cardiovascular disease.
7. Major surgery ≤ 4 weeks prior to start of study treatment.
8. Active fungal, bacterial or viral infection requiring systemic treatment.
9. History of severe bleeding disorder.

NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.