Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands		Total		Cumulative Effect, Period of Adoption, Adjustment	[3]	Comprehensive Income	Common Stock Par Value	Additional Paid-in Capital	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	[3]	Accumulated Other Comprehensive (Loss) Income
Beginning balance at Sep. 30, 2017		$ 1,755,000					$ 588	$ 1,314,039	$ 445,747			$ (5,374)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		157,916				$ 157,916			157,916
Other comprehensive (loss), net of tax		(23,782)	[1]			(23,782)						(23,782)
Comprehensive (loss) income		134,134				134,134
Stock-based compensation, net of tax		4,419					1	4,418
Reclassification due to adoption of ASU 2018-02	[2]	0							2,353			(2,353)
Cash dividends:
Cash dividends, common stock		(53,002)							(53,002)
Ending balance at Sep. 30, 2018		1,840,551					589	1,318,457	553,014			(31,509)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		167,365				167,365			167,365
Other comprehensive (loss), net of tax		45,006	[1]			45,006						45,006
Comprehensive (loss) income		$ 212,371				212,371
Accounting Standards Update [Extensible List]		us-gaap:AccountingStandardsUpdate201602Member
Stock-based compensation, net of tax		$ 4,582					1	4,581
Repurchase of common stock		(94,351)					(27)	(94,324)
Cash dividends:
Cash dividends, common stock		(62,904)							(62,904)
Ending balance at Sep. 30, 2019		1,900,249		$ (182)			563	1,228,714	657,475	$ (182)		13,497
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		(680,808)				(680,808)			(680,808)
Other comprehensive (loss), net of tax		22,408	[1]			22,408						22,408
Comprehensive (loss) income		(658,400)				$ (658,400)
Stock-based compensation, net of tax		3,705					1	3,704
Repurchase of common stock		(39,983)					(14)	(39,969)
Cash dividends:
Cash dividends, common stock		(42,456)						(8,802)	(33,654)
Ending balance at Sep. 30, 2020		$ 1,162,933					$ 550	$ 1,183,647	$ (57,169)			$ 35,905

[1] The Company's Board of Directors voted to terminate the defined benefit pension plan ("Pension Plan") effective February 1, 2018. Transfer of all Pension Plan assets, liabilities and administrative responsibilities were completed as of September 30, 2018.

[2] Reclassification due to adoption of ASU 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income.

[3] Cumulative effect adjustment relates to the adoption of ASU 2016-02, Leases (Topic 872).and related ASUs on October 1, 2019. See Note 2, "New Accounting Pronouncements," for additional information.