Note 12 - Fair Value Measurements - Schedule of Assets and Liabilities Measured on recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Sep. 30, 2023
Cash equivalents		$ 525,952
Available-for-sale securities	$ 407,382	450,211
Foreign exchange contracts		44
Net investment hedge		13,036
Total assets		989,243
Foreign exchange contracts		421
Total liabilities		421
Fair Value, Inputs, Level 1 [Member]
Cash equivalents		525,952
Available-for-sale securities		85,949
Foreign exchange contracts		0
Net investment hedge		0
Total assets		611,901
Foreign exchange contracts		0
Total liabilities		0
Fair Value, Inputs, Level 2 [Member]
Cash equivalents		0
Available-for-sale securities		364,262
Foreign exchange contracts		44
Net investment hedge		13,036
Total assets		377,342
Foreign exchange contracts		421
Total liabilities		421
Fair Value, Inputs, Level 3 [Member]
Cash equivalents		0
Available-for-sale securities		0
Foreign exchange contracts		0
Net investment hedge		0
Total assets		0
Foreign exchange contracts		0
Total liabilities		$ 0
Fair Value, Recurring [Member]
Cash equivalents	147,502
Foreign exchange contracts	201
Net investment hedge	834
Total assets	555,919
Fair Value, Recurring [Member] | Excluding Convertible Debt Securities [Member]
Available-for-sale securities	405,382
Fair Value, Recurring [Member] | Convertible Debt Securities [Member]
Available-for-sale securities	2,000
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Cash equivalents	147,253
Foreign exchange contracts	0
Net investment hedge	0
Total assets	259,886
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Excluding Convertible Debt Securities [Member]
Available-for-sale securities	112,633
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Convertible Debt Securities [Member]
Available-for-sale securities	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Cash equivalents	249
Foreign exchange contracts	201
Net investment hedge	834
Total assets	294,033
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Excluding Convertible Debt Securities [Member]
Available-for-sale securities	292,749
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Convertible Debt Securities [Member]
Available-for-sale securities	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Cash equivalents	0
Foreign exchange contracts	0
Net investment hedge	0
Total assets	2,000
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Excluding Convertible Debt Securities [Member]
Available-for-sale securities	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Convertible Debt Securities [Member]
Available-for-sale securities	$ 2,000