Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2022	Mar. 31, 2021
Basic Earnings Per Share
Net income	$ 324,999	$ 249,209	$ 296,754	$ 217,678	$ 574,208	$ 514,432
Less: Income allocated to participating securities	202		199		379	350
Income available to common shareholders	$ 324,797		$ 296,555		$ 573,829	$ 514,082
Basic weighted average shares outstanding (in shares)	136,834		129,161		135,259	128,098
Net income per share - basic (USD per share)	$ 2.37		$ 2.30		$ 4.24	$ 4.01
Diluted Earnings Per Share
Income available to common shareholders	$ 324,797		$ 296,555		$ 573,829	$ 514,082
Effect of dilutive shares	0		0		0	0
Income available to common shareholders	$ 324,797		$ 296,555		$ 573,829	$ 514,082
Basic weighted average shares outstanding (in shares)	136,834		129,161		135,259	128,098
Dilutive shares (in shares)	416		3		211	2
Diluted weighted average shares outstanding (in shares)	137,250		129,164		135,470	128,100
Net income per share - diluted (USD per share)	$ 2.37		$ 2.30		$ 4.24	$ 4.01