Earnings per Share (EPS) and Common Stock - Earnings Per Share Basic and Diluted (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
Earnings Per Share And Common Stock [Abstract]
Net Income (Loss)	$ 590,723	$ 162,644	$ 757,241	$ 244,876
Weighted-average shares outstanding—Basic	118,185	120,177	118,764	120,210
Dilutive effect of restricted stock units	368	677	513	790
Weighted-average shares outstanding—Diluted	118,553	120,854	119,277	121,000
Earnings per share—Basic	$ 5	$ 1.35	$ 6.38	$ 2.04
Earnings per share—Diluted	$ 4.98	$ 1.35	$ 6.35	$ 2.02