Shareholders' Equity - Schedule of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2020	Jun. 30, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Shareholders' equity, beginning balance	$ 6,304,415	$ 6,127,775	$ 5,750,223	$ 5,508,101	$ 5,348,195	$ 4,769,951	$ 5,750,223	$ 4,769,951
Other comprehensive income (loss) before reclassifications							(4,730)	(25,774)
Amounts reclassified from accumulated other comprehensive income							2,586	1,968
Net current-period other comprehensive income (loss)	(4,086)	890	1,052	1,147	(2,695)	(22,258)	(2,144)	(23,806)
Shareholders' equity, ending balance	6,461,471	6,304,415	6,127,775	5,641,996	5,508,101	5,348,195	6,461,471	5,641,996
Available- for-Sale Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Shareholders' equity, beginning balance			132			8,124	132	8,124
Other comprehensive income (loss) before reclassifications							202	192
Amounts reclassified from accumulated other comprehensive income							(2)	(1)
Net current-period other comprehensive income (loss)							200	191
Shareholders' equity, ending balance	332			105			332	105
Interest Rate Agreement Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Shareholders' equity, beginning balance			(114,715)			(91,771)	(114,715)	(91,771)
Other comprehensive income (loss) before reclassifications							(4,932)	(25,966)
Amounts reclassified from accumulated other comprehensive income							2,588	1,969
Net current-period other comprehensive income (loss)							(2,344)	(23,997)
Shareholders' equity, ending balance	(117,059)			(115,768)			(117,059)	(115,768)
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Shareholders' equity, beginning balance	(112,641)	(113,531)	(114,583)	(116,810)	(114,115)	(83,647)	(114,583)	(83,647)
Net current-period other comprehensive income (loss)	(4,086)	890	1,052	1,147	(2,695)	(22,258)
Shareholders' equity, ending balance	$ (116,727)	$ (112,641)	$ (113,531)	$ (115,663)	$ (116,810)	(114,115)	$ (116,727)	(115,663)
Cumulative effect of accounting change
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Shareholders' equity, beginning balance						(8,210)		(8,210)
Cumulative effect of accounting change | Available- for-Sale Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Shareholders' equity, beginning balance						(8,210)		(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		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)