Accumulated Other Comprehensive Income (Loss) - Reclassification out of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	$ 1,694,208	$ 1,807,142	$ 1,862,353	$ 1,884,305
Other comprehensive income before reclassifications	1,569	1,542	(16,956)	(848)
Balance	1,686,732	1,838,381	1,686,732	1,838,381
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance			(18,984)
Other comprehensive income before reclassifications			(2,317)
Balance	(21,301)		(21,301)
Derivative Financial Instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance			(1,612)
Other comprehensive income before reclassifications			(14,639)
Balance	(16,251)		(16,251)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(39,121)	(19,640)	(20,596)	(17,250)
Balance	$ (37,552)	$ (18,098)	$ (37,552)	$ (18,098)