Segment Information - Research and Development and Selling, General and Administrative Expenses (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Segment Reporting Information [Line Items]
Stock compensation	$ 19,590	$ 14,175
Depreciation/amortization	6,000	4,800
Total research and development expense	177,203	137,002
Total general and administrative expense	46,021	26,910
Research and development
Segment Reporting Information [Line Items]
Stock compensation	6,376	6,846
General and administrative expense
Segment Reporting Information [Line Items]
Stock compensation	13,214	7,329
Operating Segment
Segment Reporting Information [Line Items]
Candidate costs	104,990	76,896
R&D discovery costs	21,829	12,936
Salaries	30,039	27,145
Facilities related	8,102	7,750
Total research and development expense, excluding non-cash expense	164,960	124,727
Salaries	11,940	7,331
Professional, outside services, and other	18,900	10,126
Facilities related	1,663	1,285
Total general and administrative expense, excluding non-cash expense	32,503	18,742
Total research and development expense	177,203	137,002
Total general and administrative expense	46,021	26,910
Operating Segment | Research and development
Segment Reporting Information [Line Items]
Stock compensation	6,357	7,549
Depreciation/amortization	5,886	4,726
Operating Segment | General and administrative expense
Segment Reporting Information [Line Items]
Stock compensation	13,014	7,659
Depreciation/amortization	$ 504	$ 509