Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Basic and Diluted Earnings Per Share from continuing operations
Income from continuing operations					$ 35,853	$ 70,808	$ 162,012	$ 114,038	$ 603,064	$ 382,711	$ 345,542
Less: Income from continuing operations allocated to participating securities									580	475	538
Income from continuing operations available to common shareholders									$ 602,484	$ 382,236	$ 345,004
Basic and diluted weighted average shares outstanding (in shares)									111,012	106,100	103,524
Income from continuing operations per share — Basic and Diluted (in dollars per share)					$ 0.34	$ 0.67	$ 1.52	$ 1.08	$ 5.43	$ 3.60	$ 3.33
Basic and Diluted Earnings Per Share from discontinued operations
Income from discontinued operations									$ 0	$ 13,710	$ 4,562
Less: Income from discontinued operations allocated to participating securities									0	12	8
Income from discontinued operations available to common shareholders									$ 0	$ 13,698	$ 4,554
Basic and diluted weighted average shares outstanding (in shares)									111,012	106,100	103,524
Income from discontinued operations per share - Basic and Diluted (in dollars per share)					0.00	0.00	0.03	0.11	$ 0.00	$ 0.13	$ 0.05
Net income per share - basic and diluted (in dollars per share)	$ 0.35	$ 0.64	$ 1.60	$ 2.89	$ 0.34	$ 0.67	$ 1.55	$ 1.19	$ 5.43	$ 3.73	$ 3.38