First Trust Equity Market Neutral ETF S000067481 [Member] C000216993 [Member] ICE BofA 3-Month U.S. Treasury Bill Index (reflects no deduction for fees, expenses or taxes)[Member] S&P 500® Index (reflects no deduction for fees, expenses or taxes)[Member] Authorized Participant Concentration Risk [Member] Cash Transactions Risk [Member] Commodity Regulatory Risk [Member] Counterparty Risk [Member] Current Market Conditions Risk [Member] Cyber Security Risk [Member] Depositary Receipts Risk [Member] Derivatives Risk [Member] Equity Securities Risk [Member] ETF Risk [Member] Index Or Model Constituent Risk [Member] Large Capitalization Companies Risk [Member] Leverage Risk [Member] Liquidity Risk [Member] Management Risk [Member] Market Maker Risk [Member] Market Risk [Member] Risk Nondiversified [Member] Non US Securities Risk [Member] Operational Risk [Member] OTC Derivatives Risk [Member] Portfolio Turnover Risk [Member] Premium Discount Risk [Member] Short Sales Risk [Member] Significant Exposure Risk [Member] Smaller Companies Risk [Member] Special Tax Risk [Member] Swap RIC Tax Risk [Member] Total Return Swap Risk [Member] Trading Issues Risk [Member] Valuation Risk [Member] Volatility Risk [Member]