3.22.4 html 74 54 1 false 54 0 false 4 false false R1.htm 995470 - Disclosure - N-2 Sheet http://xbrl.sec.gov/cef/role/N2 N-2 Cover 1 false false All Reports Book All Reports gnt-ncsr_123122.htm ex99-a1.htm ex99-a2.htm ex99-b.htm ex99-c.htm gnt-20221231.xsd gnt-20221231_def.xml gnt-20221231_lab.xml gnt-20221231_pre.xml gntncsr123122001.jpg gntncsr123122002.jpg gntncsr123122003.jpg gntncsr123122004.jpg http://xbrl.sec.gov/cef/2022 http://xbrl.sec.gov/dei/2022 true false