| Amount of unrealized gain (loss) on investment in marketable security, excluding other-than-temporary impairment (OTTI). | en-US | http://www.xbrl.org/2003/role/documentation | http://www.xbrl.org/2003/role/link |
| Marketable Securities, Unrealized Gain (Loss), Excluding Other-than-temporary Impairment Loss | en-US | http://www.xbrl.org/2003/role/label | http://www.xbrl.org/2003/role/link |
| Marketable Securities, Unrealized Gain (Loss), Excluding Other than Temporary Impairments, Total | en-US | http://www.xbrl.org/2003/role/totalLabel | http://www.xbrl.org/2003/role/link |