Defiance Helium and Strategic Gases ETF Specialty Gas Industry Risk [Member] Foreign Investment Risk [Member] Depositary Receipt Risk [Member] Equity Market Risk [Member] Focused Portfolio Risk [Member] Index Strategy Risk [Member] Data Risk [Member] Passive Investment Risk [Member] Tracking Error Risk [Member] Concentration Risk [Member] Management Risk [Member] Risks Related to Changes in Government Policies and Institutions [Member] Derivatives Risk [Member] Options Contracts [Member] Swap Agreements [Member] Equity Total Return Swaps [Member] Counterparty Risk [Member] ETF Risks [Member] Authorized Participants, Market Makers, and Liquidity Providers Concentration Risk [Member] Cash Redemption Risk [Member] Costs of Buying or Selling Shares [Member] Shares May Trade at Prices Other Than NAV [Member] Trading [Member] Liquidity Risk [Member] Economic and Market Risk [Member] High Portfolio Turnover Risk [Member] Liquidity Risk 1 [Member] Market Capitalization Risk [Member] Large-Capitalization Investing [Member] Mid-Capitalization Investing [Member] Small-Capitalization Investing [Member] Money Market Instrument Risk [Member] New Fund Risk [Member] Operational Risk [Member] Newly Public Company Risk [Member] Tax Risk [Member] Underlying Index Risk [Member] Defiance Helium and Strategic Gases ETF [Member] Defiance Helium and Strategic Gases ETF Defiance Helium and Strategic Gases ETF Underlying Index Risk. Tax Risk. Newly Public Company Risk. Operational Risk. New Fund Risk. Money Market Instrument Risk. Small-Capitalization Investing. Mid-Capitalization Investing. Large-Capitalization Investing. Market Capitalization Risk. Liquidity Risk. Liquidity Risk 1. High Portfolio Turnover Risk. Economic and Market Risk. Trading. Shares May Trade at Prices Other Than NAV. Costs of Buying or Selling Shares. Cash Redemption Risk. Authorized Participants, Market Makers, and Liquidity Providers Concentration Risk. ETF Risks. Counterparty Risk. Equity Total Return Swaps. Swap Agreements. Options Contracts. Derivatives Risk. Risks Related to Changes in Government Policies and Institutions. Management Risk. Concentration Risk. Tracking Error Risk. Passive Investment Risk. Data Risk. Index Strategy Risk. Focused Portfolio Risk. Equity Market Risk. Depositary Receipt Risk. Foreign Investment Risk. Specialty Gas Industry Risk.