The purpose of this study is to provide nephrologists with additional clinical evidence regarding the efficacy and safety of Acthar in subjects with treatment-resistant idiopathic membranous nephropathy. Approximately sixty (60) subjects will be randomized in this double-blind, parallel-group, placebo-controlled, multicenter study comparing Acthar and Placebo administered 2 times per week for a 24-week treatment period followed by a 24-week observation period. The primary objective of this study is to assess the proportion of treatment-resistant subjects (defined as subjects who either have had no response or have suffered a relapse after achieving a partial response to their most recent standard treatment regimen) who have a complete or partial remission of proteinuria in nephrotic syndrome due to idiopathic membranous nephropathy after 24 weeks of treatment.