Stock-Based Employee Benefit Plans - Assumptions Used to Estimate Fair Value of Market Stock Units (Details) - Market stock units (MSUs)	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility in FICO’s stock price	36.30%	47.30%	42.30%
Expected volatility in Russell 3000 Index	18.20%	26.00%	23.30%
Correlation between FICO and the Russell 3000 Index	60.30%	73.50%	74.70%
Risk-free interest rate	4.39%	4.02%	0.97%
Average expected dividend yield	0.00%	0.00%	0.00%