FT Vest Gold Strategy Quarterly Buffer ETF S000070088 [Member] C000222997 [Member] LBMA Gold Price (reflects no deduction for fees, expenses or taxes)[Member] S&P 500® Index (reflects no deduction for fees, expenses or taxes)[Member] Absence Of An Active Market Risk [Member] Buffered Loss Risk [Member] Cap Change Risk [Member] Capped Upside Risk [Member] Cash Transactions Risk [Member] Commodities Risk [Member] Counterparty Risk [Member] Credit Risk [Member] Current Market Conditions Risk [Member] Cyber Security Risk [Member] Debt Securities Risk [Member] Derivatives Risk [Member] Flex Options Risk [Member] Flex Options Valuation Risk [Member] Income Risk [Member] Index Or Model Constituent Risk [Member] Inflation Risk [Member] Interest Rate Risk [Member] Management Risk [Member] Market Risk [Member] Risk Nondiversified [Member] Operational Risk [Member] Premium Discount Risk [Member] Significant Exposure Risk [Member] Subsidiary Investment Risk [Member] Target Outcome Period Risk [Member] Tax Risk [Member] Trading Issues Risk [Member] Underlying ETF Concentration Risk [Member] Underlying ETF Gold Risk [Member] Underlying ETF Risk [Member] US Government Securities Risk [Member]