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, 2018	$ 90,576	$ 820,378	$ 1,174,245	$ (75,835)	$ 2,009,364
Net income			16,924		16,924
Dividends declared			(39,014)		(39,014)
Issuance of common stock under dividend reinvestment plan	59	3,976			4,035
Repurchase of stock				(1,857)	(1,857)
Equity compensation plan	67	(67)
Exercise of stock options	39	1,136			1,175
Stock-based compensation		1,929	42		1,971
Other		(13)			(13)
Balance at Mar. 31, 2019	90,741	827,339	1,152,197	(77,692)	1,992,585
Balance at Dec. 31, 2018	90,576	820,378	1,174,245	(75,835)	2,009,364
Net income					160,316
Balance at Sep. 30, 2019	109,471	2,633,193	1,197,600	(77,702)	3,862,562
Balance at Mar. 31, 2019	90,741	827,339	1,152,197	(77,692)	1,992,585
Net income			54,903		54,903
Dividends declared			(47,249)		(47,249)
Stock issued to finance pending acquisition	18,685	1,245,440			1,264,125
Proceeds from stock purchase contract issued under tangible equity units		557,837			557,837
Issuance of common stock under dividend reinvestment plan	5	380			385
Repurchase of stock				(2)	(2)
Equity compensation plan	3	(3)
Exercise of stock options	10	361			371
Stock-based compensation		2,129	(98)		2,031
Other		(212)			(212)
Balance at Jun. 30, 2019	109,444	2,633,271	1,159,753	(77,694)	3,824,774
Net income			88,489		88,489
Dividends declared			(50,558)		(50,558)
Expenses incurred for private placement issuance of common stock		(1,474)			(1,474)
Issuance of common stock under dividend reinvestment plan	5	394			399
Issuance of common stock from stock purchase contracts	15	(15)
Repurchase of stock				(8)	(8)
Equity compensation plan	2	(2)
Exercise of stock options	5	184			189
Stock-based compensation		1,774	(84)		1,690
Other		(939)			(939)
Balance at Sep. 30, 2019	109,471	2,633,193	1,197,600	(77,702)	3,862,562
Retained earnings					1,210,072
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 under dividend reinvestment plan	43	4,019			4,062
Issuance of common stock from stock purchase contracts	1,168	(1,168)
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					$ 1,220,790