Consolidated Statement of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Cumulative effect adjustment related to ASU adoption	[1]	Common Stock Par Value	Additional Paid-in Capital	Retained Earnings	Retained Earnings Cumulative effect adjustment related to ASU adoption	[1]	Accumulated Other Comprehensive (Loss) Income
Beginning balance at Sep. 30, 2018	$ 1,840,551			$ 589	$ 1,318,457	$ 553,014			$ (31,509)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	117,080					117,080
Other comprehensive income, net of tax	40,744								40,744
Total comprehensive income (loss)	157,824
Stock-based compensation, net of tax	3,264			1	3,263
Repurchase common stock	(74,659)			(21)	(74,638)
Common stock cash dividends	(45,852)					(45,852)
Ending balance at Jun. 30, 2019	1,881,128			569	1,247,082	624,242			9,235
Beginning balance at Mar. 31, 2019	1,852,394			569	1,245,657	614,540			(8,372)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	26,783					26,783
Other comprehensive income, net of tax	17,607								17,607
Total comprehensive income (loss)	44,390
Stock-based compensation, net of tax	1,425			0	1,425
Common stock cash dividends	(17,081)					(17,081)
Ending balance at Jun. 30, 2019	1,881,128			569	1,247,082	624,242			9,235
Beginning 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 (loss) income	(691,944)					(691,944)
Other comprehensive income, net of tax	31,660								31,660
Total comprehensive income (loss)	(660,284)
Stock-based compensation, net of tax	2,750			1	2,749
Repurchase common stock	(39,983)			(14)	(39,969)
Common stock cash dividends	(41,906)				(8,252)	(33,654)
Ending balance at Jun. 30, 2020	1,160,644			550	1,183,242	(68,305)			45,157
Beginning balance at Mar. 31, 2020	1,153,464			550	1,190,381	(73,705)			36,238
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	5,400					5,400
Other comprehensive income, net of tax	8,919								8,919
Total comprehensive income (loss)	14,319
Stock-based compensation, net of tax	1,113				1,113
Common stock cash dividends	(8,252)				(8,252)
Ending balance at Jun. 30, 2020	$ 1,160,644			$ 550	$ 1,183,242	$ (68,305)			$ 45,157

[1] Related to the Company's adoption of ASU 2016-02 and subsequent related ASUs on October 1, 2019. See Note 2, "New Accounting Pronouncements," for additional information.