Shareholders' Equity - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Shareholders' equity, beginning balance	$ 5,750,223	$ 4,769,951	$ 3,898,666
Other comprehensive income before reclassifications	53,349	(25,747)
Amounts reclassified from accumulated other comprehensive income	3,645	3,021
Net current-period other comprehensive income	56,994	(22,726)	44,541
Shareholders' equity, ending balance	6,791,203	5,750,223	4,769,951
Available- for-Sale Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Shareholders' equity, beginning balance	132	8,124
Other comprehensive income before reclassifications	108	219
Amounts reclassified from accumulated other comprehensive income	(2)	(1)
Net current-period other comprehensive income	106	218
Shareholders' equity, ending balance	238	132	8,124
Interest Rate Agreement Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Shareholders' equity, beginning balance	(114,715)	(91,771)
Other comprehensive income before reclassifications	53,241	(25,966)
Amounts reclassified from accumulated other comprehensive income	3,647	3,022
Net current-period other comprehensive income	56,888	(22,944)
Shareholders' equity, ending balance	(57,827)	(114,715)	(91,771)
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Shareholders' equity, beginning balance	(114,583)	(83,647)	(105,254)
Net current-period other comprehensive income	56,994	(22,726)	44,541
Shareholders' equity, ending balance	(57,589)	(114,583)	(83,647)
Cumulative effect of accounting change | Available- for-Sale Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Shareholders' equity, beginning balance	(8,210)
Shareholders' equity, ending balance		(8,210)
Cumulative effect of accounting change | Interest Rate Agreement Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Shareholders' equity, beginning balance	0
Shareholders' equity, ending balance		0
Cumulative effect of accounting change | Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Shareholders' equity, beginning balance	$ (8,210)	(8,210)	(22,934)
Shareholders' equity, ending balance		$ (8,210)	$ (8,210)