Senior Notes (Detail) - USD ($)	Dec. 17, 2021	Dec. 06, 2019	May 08, 2018	Jun. 30, 2023	Sep. 30, 2022
Debt Instrument [Line Items]
Carrying value of Senior Notes				$ 1,300,000,000	$ 1,300,000,000
Fair value of Senior Notes				1,210,000,000	1,148,750,000
Senior Notes
Debt Instrument [Line Items]
Debt issuance costs				12,200,000	14,300,000
May 2018 Senior Notes
Debt Instrument [Line Items]
Senior Notes issued in a private placement to a group of institutional investors			$ 400,000,000
Carrying value of Senior Notes				400,000,000	400,000,000
Fair value of Senior Notes				391,000,000	381,500,000
Debt instrument, maturity date			May 15, 2026
Debt Instrument, Interest Rate, Stated Percentage			5.25%
Dec 2019 Senior Notes
Debt Instrument [Line Items]
Carrying value of Senior Notes				900,000,000	900,000,000
Fair value of Senior Notes				$ 819,000,000	$ 767,250,000
Senior Notes December Twenty one
Debt Instrument [Line Items]
Senior Notes issued in a private placement to a group of institutional investors	$ 550,000,000
Debt instrument, maturity date	Jun. 15, 2028
Debt Instrument, Interest Rate, Stated Percentage	4.00%
Senior Notes 2019
Debt Instrument [Line Items]
Senior Notes issued in a private placement to a group of institutional investors		$ 350,000,000
Debt instrument, maturity date		Jun. 15, 2028
Debt Instrument, Interest Rate, Stated Percentage		4.00%