Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Numerator for diluted and basic earnings per share:
Net income	$ 264,458	$ 162,615	$ 422,831	$ 315,143
Denominator — share:
Basic weighted-average shares (in shares)	23,628	24,389	23,676	24,383
Effect of dilutive securities (in shares)	120	296	178	373
Diluted weighted-average shares (in shares)	23,748	24,685	23,854	24,756
Earnings per share:
Basic (in dollars per share)	$ 11.19	$ 6.67	$ 17.86	$ 12.92
Diluted (in dollars per share)	$ 11.14	$ 6.59	$ 17.73	$ 12.73