Shareholders' Equity - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Shareholders' equity, beginning balance	$ 6,791,203	$ 5,750,223	$ 4,769,951
Other comprehensive income (loss) before reclassifications	122,826	53,349
Amounts reclassified from accumulated other comprehensive income	4,566	3,645
Net current-period other comprehensive income (loss)	127,392	56,994	(22,726)
Shareholders' equity, ending balance	7,906,889	6,791,203	5,750,223
Available- for-Sale Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Shareholders' equity, beginning balance	238	132
Other comprehensive income (loss) before reclassifications	(191)	108
Amounts reclassified from accumulated other comprehensive income	0	(2)
Net current-period other comprehensive income (loss)	(191)	106
Shareholders' equity, ending balance	47	238	132
Interest Rate Agreement Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Shareholders' equity, beginning balance	(57,827)	(114,715)
Other comprehensive income (loss) before reclassifications	123,017	53,241
Amounts reclassified from accumulated other comprehensive income	4,566	3,647
Net current-period other comprehensive income (loss)	127,583	56,888
Shareholders' equity, ending balance	69,756	(57,827)	(114,715)
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Shareholders' equity, beginning balance	(57,589)	(114,583)	(83,647)
Net current-period other comprehensive income (loss)	127,392	56,994	(22,726)
Shareholders' equity, ending balance	$ 69,803	$ (57,589)	$ (114,583)