CONSOLIDATED STATEMENTS OF COMMON STOCK EQUITY - USD ($) $ in Thousands		Total	Common Stock	Premium on Common Stock	Accumulated Other Comprehensive (Loss) Income	Treasury Stock And Other	Retained Earnings
Beginning Balance (in shares) at Sep. 30, 2015			85,531,000
Beginning Balance at Sep. 30, 2015		$ 1,106,956	$ 220,838	$ 209,931	$ (9,394)	$ (92,164)	$ 777,745
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		131,672					131,672
Other comprehensive loss		(5,761)			(5,761)
Common stock issued:
Incentive compensation plan (in shares)			325,000
Incentive compensation plan		9,399	$ 816	8,583
Divident reinvestment plan (in shares)	[1]		471,000
Dividend reinvestment plan	[1]	16,063		(2,879)		18,942
Cash dividend declared ($1.11 per share in 2018, $1.0375 per share in 2017, and $.975 per share in 2016)		(83,861)					(83,861)
Treasury stock and other (in shares)			(241,000)
Treasury stock and other		(7,877)		(55)		(7,822)
Ending Balance (in shares) at Sep. 30, 2016			86,086,000
Ending Balance at Sep. 30, 2016		1,166,591	$ 221,654	215,580	(15,155)	(81,044)	825,556
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		132,065					132,065
Other comprehensive loss		11,899			11,899
Common stock issued:
Incentive compensation plan (in shares)			241,000
Incentive compensation plan		5,694	$ 604	5,090
Divident reinvestment plan (in shares)	[1]		472,000
Dividend reinvestment plan	[1]	17,622		(946)		18,568
Cash dividend declared ($1.11 per share in 2018, $1.0375 per share in 2017, and $.975 per share in 2016)		(89,637)					(89,637)
Treasury stock and other (in shares)			(243,000)
Treasury stock and other		$ (7,591)		(28)		(7,563)
Ending Balance (in shares) at Sep. 30, 2017		86,555,507	86,556,000
Ending Balance at Sep. 30, 2017		$ 1,236,643	$ 222,258	219,696	(3,256)	(70,039)	867,984
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		233,436					233,436
Other comprehensive loss		(6,078)			(6,078)
Common stock issued:
Incentive compensation plan (in shares)			561,000
Incentive compensation plan		16,572	$ 1,403	15,169
Divident reinvestment plan (in shares)	[1]		413,000
Dividend reinvestment plan	[1]	17,094		755		16,339
Waiver discount (in shares)			1,014,000
Waiver discount		41,677	$ 2,535	39,142
Cash dividend declared ($1.11 per share in 2018, $1.0375 per share in 2017, and $.975 per share in 2016)		(97,579)					(97,579)
Treasury stock and other (in shares)			(251,000)
Treasury stock and other		$ (22,787)		(14)		(22,773)
Ending Balance (in shares) at Sep. 30, 2018		88,292,956	88,293,000
Ending Balance at Sep. 30, 2018		$ 1,418,978	$ 226,196	$ 274,748	(12,610)	$ (76,473)	1,007,117
Common stock issued:
Reclassifications of certain income tax effects to retained earnings (2)	[2]				$ (3,276)		$ 3,276

[1] Shares sold through the DRP are issued from treasury stock at average cost, which may differ from the actual market price paid.

[2] Due to the adoption of ASU No. 2018-02, an amendment to ASC 740, Income Taxes. See Note 2. Summary of Significant Accounting Policies - Recently Adopted Updates to the Accounting Standards Codification section for more details.