Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands		Total	Comprehensive Income	Common Stock Par Value	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning balance at Sep. 30, 2015		$ 1,459,346		$ 552	$ 1,201,387	$ 255,089	$ 2,318
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		121,253	$ 121,253			121,253
Other comprehensive income, net of tax		3,216	3,216				3,216
Comprehensive income		124,469	124,469
Stock-based compensation, net of tax		3,517			3,517
Common stock issued in business acquisition		107,478		35	107,443
Cash dividends:
Common stock, $0.90, $0.74, and $0.56 per share in 2018, 2017 and 2016, respectively		(31,419)				(31,419)
Ending balance at Sep. 30, 2016		1,663,391		587	1,312,347	344,923	5,534
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustment	[1]	263			751	(488)
Net income		144,786	144,786			144,786
Other comprehensive income, net of tax		(10,908)	(10,908)				(10,908)
Comprehensive income		133,878	133,878
Stock-based compensation, net of tax		6,547		2	6,545
Repurchase of common stock		(5,605)		(1)	(5,604)
Cash dividends:
Common stock, $0.90, $0.74, and $0.56 per share in 2018, 2017 and 2016, respectively		(43,474)				(43,474)
Ending 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 income, net of tax		(23,782)	(23,782)				(23,782)
Comprehensive income		134,134	$ 134,134
Stock-based compensation, net of tax		4,419		1	4,418
Reclassification from AOCI to retained earnings	[2]	0				2,353	(2,353)
Cash dividends:
Common stock, $0.90, $0.74, and $0.56 per share in 2018, 2017 and 2016, respectively		(53,002)				(53,002)
Ending balance at Sep. 30, 2018		$ 1,840,551		$ 589	$ 1,318,457	$ 553,014	$ (31,509)

[1] Cumulative effect adjustment relates to adoption of ASU 2016-09, Compensation - Stock Based Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting.

[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. See Note 1, New Accounting Pronouncements and Note 18, Income Taxes, for additional information.