The use of agile development methodologies in the software industry has increased significantly over the past decade. This has led to efforts to adjust these methodologies to enterprise products and complex systems' development, and specifically to combine the requirement of minimalism with the need for well-defined up-front architecture artifacts. Nevertheless, in many cases, architecture is accompanied with extensive documentation that requires significant effort to review and maintain throughout the development lifecycle. This paper presents a case study that aims at identifying difficulties architects and other stakeholders encounter when dealing with architecture documentation in agile development. The findings indicate that the architecture specification document is usually very long, complex, and not self-explanatory. In order to adjust the architecture documentation to the lean and minimal documentation approach of agile processes, we propose a considerably shorter abstract specification document, requiring reduced documentation efforts and resulting in a lean documentation that is easier to review, update, and communicate.