First Trust Nasdaq Pharmaceuticals ETF Investment Strategy - First Trust Nasdaq Pharmaceuticals ETF	Mar. 31, 2025
Prospectus [Line Items]
Strategy [Heading]	<span style="color:#000000;font-family:Arial;font-size:9.90pt;font-weight:bold;">Principal Investment Strategies</span>
Strategy Narrative [Text Block]	The Fund will normally invest at least 90% of its net assets (including investment borrowings) in the securities that comprise the Index. The Fund, using an indexing investment approach, attempts to replicate, before fees and expenses, the performance of the Index. The Index is owned and is developed, maintained and sponsored by Nasdaq, Inc. (the “Index Provider”). The Index Provider may, from time to time, exercise reasonable discretion as it deems appropriate in order to ensure Index integrity. According to the Index Provider, the Index is designed to provide exposure to the 30 to 50 top factor-ranked securities from U.S. pharmaceutical and biotechnology companies. The Index’s initial selection universe consists of the component securities of the Nasdaq US BenchmarkTM Index that have been classified as comprising the pharmaceuticals and biotechnology subsectors according to the Industry Classification Benchmark (the “ICB”). According to the ICB, companies comprising these subsectors include (i) companies engaged in research into and development of biological substances for the purposes of drug discovery and diagnostic development, and which derive the majority of their revenue from either the sale or licensing of these drugs and diagnostic tools; and (ii) manufacturers of prescription or over-the-counter drugs, such as aspirin, cold remedies and birth control pills, including vaccine producers, but excluding vitamin producers. The Nasdaq US BenchmarkTM Index is a float adjusted market capitalization-weighted index designed to track the performance of securities assigned to the U.S. The Fund may invest in depositary receipts and companies with various market capitalizations. According to the Index Provider, in order to be eligible for inclusion in the Index, a security must meet certain size, float and liquidity standards of the Index. Securities from the same issuer will be subject to conditions controlled by the Index Provider to determine Index eligibility. The Index Provider then ranks the remaining eligible stocks based on the aggregate of the following four factors: (1) gross income; (2) return on assets; (3) momentum; and (4) cash flow. The cash flow factor is given limited weight and may serve as a tiebreaker. The Index Provider selects the securities that either have factor scores of 30 or lower, or rank among the top 75% with factor scores not exceeding 50. This ensures the Index consists of 30 to 50 Index securities. The Index assigns security weights based upon cash flow. However, the Index will not assign a security weight of greater than 8% and no more than five securities may be assigned the maximum 8% weight. All other securities are capped at 4% and no security may have a weight less than 0.50%. The Index is rebalanced and reconstituted semi-annually and the Fund will make corresponding changes to its portfolio shortly after the Index changes are made public. The Fund will be concentrated in an industry or a group of industries to the extent that the Index is so concentrated. As of June 30, 2025, the Index was composed of 49 securities with market capitalization ranges from $1.68 billion to $699.81 billion. As of June 30, 2025, the Fund had significant investments in health care companies, although this may change from time to time. The Fund's investments will change as the Index changes and, as a result, the Fund may have significant investments in jurisdictions or investment sectors that it may not have had as of June 30, 2025. To the extent the Fund invests a significant portion of its assets in a given jurisdiction or investment sector, the Fund may be exposed to the risks associated with that jurisdiction or investment sector.
Strategy Portfolio Concentration [Text]	<span style="font-family:Arial;font-size:9.00pt;">The Fund will be concentrated in an industry or a group of industries to the extent </span><span style="font-family:Arial;font-size:9.00pt;margin-left:0%;">that the Index is so concentrated. As of June </span><span style="font-family:Arial;font-size:9.00pt;">30, 2025, the Index was composed of 49 securities with market capitalization </span><span style="font-family:Arial;font-size:9.00pt;margin-left:0%;">ranges from $</span><span style="font-family:Arial;font-size:9.00pt;">1.68 billion to $699.81 billion. As of June 30, 2025, the Fund had significant investments in health care </span><span style="font-family:Arial;font-size:9.00pt;margin-left:0%;">companies, although this may change from time to time.</span>

First Trust Nasdaq Pharmaceuticals ETF Investment Strategy - First Trust Nasdaq Pharmaceuticals ETF

Mar. 31, 2025

Principal Investment Strategies

The Fund will normally invest at least 90% of its net assets (including investment borrowings) in the securities that comprise the Index. The Fund, using an indexing investment approach, attempts to replicate, before fees and expenses, the performance of the Index. The Index is owned and is developed, maintained and sponsored by Nasdaq, Inc. (the “Index Provider”). The Index Provider may, from time to time, exercise reasonable discretion as it deems appropriate in order to ensure Index integrity. According to the Index Provider, the Index is designed to provide exposure to the 30 to 50 top factor-ranked securities from U.S. pharmaceutical and biotechnology companies. The Index’s initial selection universe consists of the component securities of the Nasdaq US BenchmarkTM Index that have been classified as comprising the pharmaceuticals and biotechnology subsectors according to the Industry Classification Benchmark (the “ICB”). According to the ICB, companies comprising these subsectors include (i) companies engaged in research into and development of biological substances for the purposes of drug discovery and diagnostic development, and which derive the majority of their revenue from either the sale or licensing of these drugs and diagnostic tools; and (ii) manufacturers of prescription or over-the-counter drugs, such as aspirin, cold remedies and birth control pills, including vaccine producers, but excluding vitamin producers. The Nasdaq US BenchmarkTM Index is a float adjusted market capitalization-weighted index designed to track the performance of securities assigned to the U.S. The Fund may invest in depositary receipts and companies with various market capitalizations. According to the Index Provider, in order to be eligible for inclusion in the Index, a security must meet certain size, float and liquidity standards of the Index. Securities from the same issuer will be subject to conditions controlled by the Index Provider to determine Index eligibility. The Index Provider then ranks the remaining eligible stocks based on the aggregate of the following four factors: (1) gross income; (2) return on assets; (3) momentum; and (4) cash flow. The cash flow factor is given limited weight and may serve as a tiebreaker. The Index Provider selects the securities that either have factor scores of 30 or lower, or rank among the top 75% with factor scores not exceeding 50. This ensures the Index consists of 30 to 50 Index securities. The Index assigns security weights based upon cash flow. However, the Index will not assign a security weight of greater than 8% and no more than five securities may be assigned the maximum 8% weight. All other securities are capped at 4% and no security may have a weight less than 0.50%. The Index is rebalanced and reconstituted semi-annually and the Fund will make corresponding changes to its portfolio shortly after the Index changes are made public. The Fund will be concentrated in an industry or a group of industries to the extent that the Index is so concentrated. As of June 30, 2025, the Index was composed of 49 securities with market capitalization ranges from $1.68 billion to $699.81 billion. As of June 30, 2025, the Fund had significant investments in health care companies, although this may change from time to time. The Fund's investments will change as the Index changes and, as a result, the Fund may have significant investments in jurisdictions or investment sectors that it may not have had as of June 30, 2025. To the extent the Fund invests a significant portion of its assets in a given jurisdiction or investment sector, the Fund may be exposed to the risks associated with that jurisdiction or investment sector.

Strategy Portfolio Concentration [Text]

The Fund will be concentrated in an industry or a group of industries to the extent that the Index is so concentrated. As of June 30, 2025, the Index was composed of 49 securities with market capitalization ranges from $1.68 billion to $699.81 billion. As of June 30, 2025, the Fund had significant investments in health care companies, although this may change from time to time.