Additional Financial Information - Additional Information (Detail) - USD ($) $ in Thousands							3 Months Ended		9 Months Ended
	Jun. 28, 2019	Mar. 26, 2019	Dec. 20, 2018	Aug. 07, 2018	May 07, 2018	Jan. 08, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Supplemental Cash Flow Information [Abstract]
Accrued interest paid							$ 50,000	$ 41,000	$ 120,000	$ 126,000
Income taxes paid net of refunds							$ 22,000	15,000	$ 40,000	33,000
Special cash dividends	$ 31,250	$ 31,250	$ 31,250	$ 500,000	$ 300,000	$ 125,000
Special cash dividends, date to be paid	Jul. 05, 2019	Apr. 05, 2019	Jan. 04, 2019	Aug. 10, 2018	May 11, 2018	Jan. 12, 2018
Special cash dividends, date of record				Aug. 07, 2018	May 07, 2018	Jan. 11, 2018
Sale of common shares, consideration received								504,000
Estimated pre-tax gain, net of estimated royalty expense and other related cost								378,000		378,000
Estimated advance royalty recoveries								16,000		$ 16,000
Estimated tax expense associated with net income on sale of shares								$ 77,000