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, 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