Consolidated Statements Of Equity - USD ($) $ in Thousands	Common Stock [Member]	Capital In Excess Of Par Value [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Total
Balance at Dec. 31, 2019	$ 111,935	$ 2,636,555	$ 1,210,072	$ (77,702)	$ 3,880,860
Net income			51,781		51,781
Dividends declared			(52,205)		(52,205)
Issuance of common stock from private placement	10,831	719,304			730,135
Issuance of common stock from stock purchase contracts	1,168	(1,168)
Issuance of common stock under dividend reinvestment plan	43	4,019			4,062
Repurchase of stock				(4,339)	(4,339)
Equity compensation plan	112	(112)
Exercise of stock options	28	922			950
Stock-based compensation		2,072	(147)		1,925
Other		(6)			(6)
Balance at Mar. 31, 2020	124,117	3,361,586	1,209,501	(82,041)	4,613,163
Balance at Dec. 31, 2019	111,935	2,636,555	1,210,072	(77,702)	3,880,860
Net income					182,142
Balance at Sep. 30, 2020	124,228	3,372,376	1,220,790	(81,641)	4,635,753
Balance at Mar. 31, 2020	124,117	3,361,586	1,209,501	(82,041)	4,613,163
Net income			74,629		74,629
Dividends declared			(57,414)		(57,414)
Expenses incurred for private placement issuance of common stock		(834)			(834)
Issuance of common stock under dividend reinvestment plan	50	3,949			3,999
Repurchase of stock				(4)	(4)
Equity compensation plan	2	(2)
Exercise of stock options	2	115			117
Stock-based compensation		1,918	(94)		1,824
Other		(37)		91	54
Balance at Jun. 30, 2020	124,171	3,366,695	1,226,622	(81,954)	4,635,534
Net income			55,732		55,732
Dividends declared			(61,460)		(61,460)
Issuance of common stock under dividend reinvestment plan	52	4,209			4,261
Repurchase of stock				(2)	(2)
Equity compensation plan	3	(3)
Exercise of stock options	2	146			148
Stock-based compensation		2,082	(104)		1,978
Other		(753)		315	(438)
Balance at Sep. 30, 2020	124,228	3,372,376	1,220,790	(81,641)	4,635,753
Retained earnings					1,261,862
Balance at Dec. 31, 2020	124,285	3,379,057	1,261,862	(81,327)	4,683,877
Net income			183,689		183,689
Dividends declared			(61,520)		(61,520)
Issuance of common stock under dividend reinvestment plan	49	4,112			4,161
Repurchase of stock				(3,262)	(3,262)
Equity compensation plan	97	(97)
Exercise of stock options	10	704			714
Stock-based compensation		2,631	(174)		2,457
Other		(31)		256	225
Balance at Mar. 31, 2021	124,441	3,386,376	1,383,857	(84,333)	4,810,341
Balance at Dec. 31, 2020	124,285	3,379,057	1,261,862	(81,327)	4,683,877
Net income					315,106
Balance at Sep. 30, 2021	127,990	3,698,095	1,385,631	(83,854)	5,127,862
Balance at Mar. 31, 2021	124,441	3,386,376	1,383,857	(84,333)	4,810,341
Net income			80,914		80,914
Dividends declared			(61,584)		(61,584)
Issuance of common stock under dividend reinvestment plan	46	4,049			4,095
Repurchase of stock				(17)	(17)
Equity compensation plan	2	(2)
Exercise of stock options	11	781			792
Stock-based compensation		2,316	(146)		2,170
Other		(148)		252	104
Balance at Jun. 30, 2021	124,500	3,393,372	1,403,041	(84,098)	4,836,815
Net income			50,503		50,503
Dividends declared			(67,758)		(67,758)
Issuance of common stock from stock purchase contracts	3,350	296,389			299,739
Issuance of common stock under dividend reinvestment plan	64	(64)
Issuance of common stock from forward equity sale agreement	46	4,295			4,341
Repurchase of stock				(8)	(8)
Equity compensation plan	2	(2)
Exercise of stock options	28	1,759			1,787
Stock-based compensation		2,328	(155)		2,173
Other		18		252	270
Balance at Sep. 30, 2021	$ 127,990	$ 3,698,095	$ 1,385,631	$ (83,854)	5,127,862
Retained earnings					$ 1,385,631