软件包XBRL无法下载架构

Question

XBRL包无法找到具有以下内容的现有XSD：

url <- "https://www.sec.gov/Archives/edgar/data/51143/000104746916010329/ibm-20151231.xml"
xbrl.vars <- xbrlDoAll(url, cache.dir = "XBRLcache", prefix.out = NULL, verbose = TRUE)

错误是：

Error in fileFromCache(file) : 
  Error in download.file(file, cached.file, method = "auto", quiet = !verbose) : 
  cannot download all files

In addition: Warning message:
In download.file(file, cached.file, method = "auto", quiet = !verbose) :
  URL 'https://www.sec.gov/Archives/edgar/data/51143/000104746916010329/ibm-20151231.xsd': status was '404 Not Found'

然而，XSD存在。我在OS X El Capitan上运行R 3.3.2。