Inclusion Criteria:

          -  Histologically confirmed diagnosis of Indolent non-Hodgkin's lymphoma (iNHL) in CD20
             positive patients, with histological subtype limited to:

               -  Follicular lymphoma(FL) grade1-2-3a

               -  Small lymphocytic lymphoma(SLL) with absolute lymphocyte count <5x10*9/L at study
                  entry

               -  Lymphoplasmacytoid lymphoma/Waldenström macroglobulinemia (LPL/WM)

               -  Marginal zone lymphoma (MZL) (splenic, nodal, or extra-nodal)

          -  Patients must have relapsed (recurrence after complete response or presented
             progression after partial response) after the last rituximab-, rituximab biosimilars-,
             or anti-CD20 monoclonal antibody (e.g. obinutuzumab)-containing therapy (other
             previous treatment lines after rituximab are allowed). A previous regimen is defined
             as one of the following: at least 2 months of single-agent therapy (less than 2 months
             of therapy is allowed for patients who responded to single-agent rituximab, rituximab
             biosimilars, or anti-CD20 monoclonal antibody); at least 2 consecutive cycles of
             polychemotherapy; autologous transplant; radioimmunotherapy. Previous exposure to PI3K
             is acceptable (except to copanlisib) provided there is no resistance. Patients with
             prior intolerance to PI3K inhibitors other than copanlisib are eligible.

          -  Non-WM must have at least one bi-dimensionally measurable lesion (which has not been
             previously irradiated) according to the Lugano Classification. For patients with
             splenic MZL (Marginal-zone lymphoma) this requirement may be restricted to
             splenomegaly alone since that is usually the only manifestation of measurable disease.

          -  Patients affected by WM who do not have at least one bi-dimensionally measurable
             lesion in the baseline radiologic assessment must have measurable disease, defined as
             presence of immunoglobulin M (IgM) paraprotein with a minimum IgM level ≥ 2 x upper
             limit of normal (ULN) and positive immunofixation test .

          -  Male or female patients ≥ 18 years of age

          -  Eastern Cooperative Oncology Group (ECOG) performance status ≤ 2

          -  Life expectancy of at least 3 months

          -  Availability of fresh tumor tissue and/or archival tumor tissue for central
             pathology(obtained within 5 years of the consent date) at Screening

          -  Adequate baseline laboratory values collected no more than 7 days before starting
             study treatment

          -  Left ventricular ejection fraction ≥ 45%

          -  Patients must either:

               -  have had a progression-free and treatment-free interval of at least 12 months
                  after completion of the rituximab-, rituximab biosimilars-, or anti-CD20
                  monoclonal antibody-containing treatment OR

               -  be considered unfit to receive chemotherapy on reason of age, concomitant
                  morbidities, and/or residual toxicity from previous treatments, or unwillingness
                  to receive chemotherapy. These patients must also have had a progression-free and
                  treatment-free interval of at least 6 months after completion of the last
                  rituximab-, rituximab biosimilars-, or anti-CD20 monoclonal antibody-containing
                  treatment. Patients in whom chemotherapy is contraindicated are defined by one of
                  the following features:

                    -  Age ≥ 80 years

                    -  Age < 80 years and at least 1 of the following conditions:

                         -  at least 3 grade 3 CIRS-G comorbidities OR

                         -  at least 1 grade 4 CIRS-G comorbidity (if compatible to participation
                            in the study).

        Exclusion Criteria:

          -  Histologically confirmed diagnosis of follicular lymphoma grade 3b or transformed
             disease, or chronic lymphocytic leukemia

          -  Progression free interval or treatment free interval of less than 12 months since the
             last rituximab-, rituximab biosimilars-, or anti-CD20 monoclonal antibody (e.g.
             obinutuzumab)-containing treatment(including maintenance with these drugs). For
             patients considered unwilling/unfit to receive chemotherapy : progression free
             interval or treatment free interval of less than 6 months since the last rituximab-,
             rituximab biosimilars-, or anti-CD20 monoclonal antibody-containing treatment
             (including maintenance with these drugs), as assessed by the investigator

          -  History or concurrent condition of interstitial lung disease of any severity and/or
             severely impaired lung function

          -  Known lymphomatous involvement of the central nervous system

          -  Patients with HbA1c > 8.5% at Screening

          -  Known history of human immunodeficiency virus (HIV) infection

          -  Hepatitis B (HBV) or hepatitis C (HCV). Patients positive for HBsAg or HBcAb will be
             eligible if they are negative for HBV-DNA, these patients should receive prophylactic
             antiviral therapy. Patients positive for anti- HCV antibody will be eligible if they
             are negative for HCV-RNA

          -  Documented evidence of resistance to prior treatment with idelalisib or other PI3K
             inhibitors.

          -  Prior treatment with copanlisib

          -  Cytomegalovirus (CMV) infection. Patients who are CMV PCR positive at baseline will
             not be eligible.