| Amount of unrealized gain (loss) on investments in debt and equity securities classified as available-for-sale securities. | en-US | http://www.xbrl.org/2003/role/documentation | http://www.xbrl.org/2003/role/link |
| Available-for-sale Securities, Gross Unrealized Gain (Loss) (Deprecated 2018-01-31) | en-US | http://www.xbrl.org/2003/role/label | http://www.xbrl.org/2003/role/link |
| Available-for-sale Securities, Gross Unrealized Gain (Loss), Total (Deprecated 2018-01-31) | en-US | http://www.xbrl.org/2003/role/totalLabel | http://www.xbrl.org/2003/role/link |