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, 2023	Sep. 30, 2022	Sep. 30, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility in FICO’s stock price	47.30%	42.30%	41.30%
Expected volatility in Russell 3000 Index	26.00%	23.30%	23.70%
Correlation between FICO and the Russell 3000 Index	73.50%	74.70%	77.50%
Risk-free interest rate	4.02%	0.97%	0.20%
Average expected dividend yield	0.00%	0.00%	0.00%