First Trust NASDAQ Clean Edge Smart Grid Infrastructure Index Fund Investment Objectives and Goals - First Trust NASDAQ Clean Edge Smart Grid Infrastructure Index Fund	Sep. 30, 2025
Prospectus [Line Items]
Risk/Return [Heading]	<span style="color:#000000;font-family:Arial;font-size:12.60pt;font-weight:bold;">First Trust NASDAQ</span><span style="color:#000000;font-family:Arial;font-size:7.38pt;font-weight:bold;position:relative;top:-4.25pt;">®</span><span style="color:#000000;font-family:Arial;font-size:12.60pt;font-weight:bold;"> Clean Edge</span><span style="color:#000000;font-family:Arial;font-size:7.38pt;font-weight:bold;position:relative;top:-4.25pt;">®</span><span style="color:#000000;font-family:Arial;font-size:12.60pt;font-weight:bold;"> Smart Grid Infrastructure Index Fund (GRID)</span>
Objective [Heading]	<span style="color:#000000;font-family:Arial;font-size:9.90pt;font-weight:bold;">Investment Objective</span>
Objective, Primary [Text Block]	The First Trust NASDAQ® Clean Edge® Smart Grid Infrastructure Index Fund (the “Fund”) seeks investment results that correspond generally to the price and yield (before the Fund’s fees and expenses) of an equity index called the Nasdaq Clean Edge Smart Grid InfrastructureTM Index (the “Index”).

First Trust NASDAQ Clean Edge Smart Grid Infrastructure Index Fund Investment Objectives and Goals - First Trust NASDAQ Clean Edge Smart Grid Infrastructure Index Fund

Sep. 30, 2025

First Trust NASDAQ® Clean Edge® Smart Grid Infrastructure Index Fund (GRID)

Objective [Heading]

Investment Objective

Objective, Primary [Text Block]

The First Trust NASDAQ® Clean Edge® Smart Grid Infrastructure Index Fund (the “Fund”) seeks investment results that correspond generally to the price and yield (before the Fund’s fees and expenses) of an equity index called the Nasdaq Clean Edge Smart Grid InfrastructureTM Index (the “Index”).