Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2019	Jun. 30, 2018
Basic and Diluted Earnings Per Share, Continuing Operations [Abstract]
Net income	$ 80,466	$ 214,888	$ 157,646	$ 71,193	$ 178,992	$ 314,132	$ 453,000	$ 564,317
Income allocated to participating securities	64			59			386	545
Income available to common shareholders	$ 80,402			$ 71,134			$ 452,614	$ 563,772
Basic weighted average shares outstanding	118,075			111,851			116,485	110,707
Basic net income per share	$ 0.68			$ 0.64			$ 3.89	$ 5.09
Effect of dilutive shares	$ 0			$ 0			$ 0	$ 0
Income available to common shareholders	$ 80,402			$ 71,134			$ 452,614	$ 563,772
Additional dilutive shares	355			0			188	0
Diluted weighted average shares outstanding	118,430			111,851			116,673	110,707
Diluted net income per share	$ 0.68			$ 0.64			$ 3.88	$ 5.09