Consolidated Statements of Changes in Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Capital In Excess of Par Value	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning balance, shares at Dec. 31, 2018		153,634
Beginning balance at Dec. 31, 2018	$ 1,593,147	$ 1,536	$ 1,106,641	$ 517,970	$ (33,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	113,981			113,981
Other comprehensive loss	4,280				4,280
Purchase and retirement of common stock	(88,789)	$ (17)	(9,202)	(79,570)
Purchase and retirement of common stock, shares		(1,725)
Issuance of common stock under employee stock purchase plan	1,322	$ 0	1,322
Issuance of common stock under the employee stock purchase plan, shares		32
Issuance of common stock upon exercise of stock options	7,571	$ 4	7,567
Issuance of common stock upon exercise of stock options, shares		335
Stock-based compensation	5,038		5,038
Ending balance at Mar. 31, 2019	$ 1,636,550	$ 1,523	1,111,366	552,381	(28,720)
Ending balance, shares at Mar. 31, 2019		152,276
Beginning balance, shares at Dec. 31, 2019	149,745	149,745
Beginning balance at Dec. 31, 2019	$ 1,738,778	$ 1,497	1,158,900	601,885	(23,504)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	109,242			109,242
Other comprehensive loss	(11,844)				(11,844)
Purchase and retirement of common stock	(127,432)	$ (24)	(13,767)	(113,641)
Purchase and retirement of common stock, shares		(2,433)
Issuance of common stock under employee stock purchase plan	1,106	$ 0	1,106
Issuance of common stock under the employee stock purchase plan, shares		21
Issuance of common stock upon exercise of stock options	17,487	$ 6	17,481
Issuance of common stock upon exercise of stock options, shares		570
Stock-based compensation	6,929		6,929
Ending balance at Mar. 31, 2020	$ 1,734,266	$ 1,479	$ 1,170,649	$ 597,486	$ (35,348)
Ending balance, shares at Mar. 31, 2020	147,903	147,903