private function _getInstance($pFileStr)
    {
        $filePath = $this->_configPath;
        $file     = $filePath . str_replace('-', DS, $pFileStr) . self::EXT;

        if ($this->_envPrefix) {
            $file = preg_replace('/([a-z0-9]+\.)/i', $this->_envPrefix . '$1', $file);
        }

        if (! isset($this->_instance[$file])) {
            if (is_readable($file)) {
                $this->_instance[$file] = require($file);
            } else if ($this->_envPrefix
                and $file = $filePath . str_replace('-', DS, $pFileStr) . self::EXT
                and is_readable($file)) {
                $this->_instance[$file] = require($file);
            } else {
                $this->_instance[$file] = array();
            }
        }

        return $this->_instance[$file];
    }