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, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Earnings Per Share And Common Stock [Abstract]
Net income	$ 89,679	$ 109,262	$ 135,768	$ 132,777
Weighted-average shares outstanding—Basic	117,008	116,777	117,135	116,587
Dilutive effect of restricted stock units	803	1,554	1,027	1,379
Weighted-average shares outstanding—Diluted	117,811	118,331	118,162	117,966
Earnings per share—Basic	$ 0.77	$ 0.94	$ 1.16	$ 1.14
Earnings per share—Diluted	$ 0.76	$ 0.92	$ 1.15	$ 1.13