Interim Consolidated Statements of Shareholders' Equity and Comprehensive Income (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Treasury Stock	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning balance at Dec. 31, 2019	$ 420,780	$ 448	$ 783,871	$ (4,539,154)	$ 4,499,288	$ (323,673)
Beginning balance, shares at Dec. 31, 2019		24,125,317
Stock Issued During Period, Value, Treasury Stock Reissued	(7,135)		0	(9,355)	(2,220)
Exercise of stock options and restricted stock units, shares		50,372
Treasury Stock, Value, Acquired, Cost Method	(200,000)			(200,000)
Repurchases of common stock, shares		(268,161)
Adjustment to Additional Paid in Capital, Share-Based Compensation	4,395		4,395
Net earnings	98,115				98,115
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(24,028)					(24,028)
Ending balance at Mar. 31, 2020	306,397	$ 448	788,266	(4,729,799)	4,595,183	(347,701)
Ending balance, shares at Mar. 31, 2020		23,907,528
Beginning balance at Dec. 31, 2019	$ 420,780	$ 448	783,871	(4,539,154)	4,499,288	(323,673)
Beginning balance, shares at Dec. 31, 2019		24,125,317
Exercise of stock options and restricted stock units, shares	114,109
Treasury Stock, Value, Acquired, Cost Method	$ (200,000)
Repurchases of common stock, shares	(268,161)
Net earnings	$ 224,677
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(21,932)
Ending balance at Jun. 30, 2020	450,093	$ 448	792,689	(4,717,962)	4,720,523	(345,605)
Ending balance, shares at Jun. 30, 2020		23,971,265
Beginning balance at Mar. 31, 2020	306,397	$ 448	788,266	(4,729,799)	4,595,183	(347,701)
Beginning balance, shares at Mar. 31, 2020		23,907,528
Stock Issued During Period, Value, Treasury Stock Reissued	(10,615)		0	(11,837)	(1,222)
Exercise of stock options and restricted stock units, shares		63,737
Treasury Stock, Value, Acquired, Cost Method	0			0
Repurchases of common stock, shares		0
Adjustment to Additional Paid in Capital, Share-Based Compensation	4,423		4,423
Net earnings	126,562				126,562
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	2,096					2,096
Ending balance at Jun. 30, 2020	450,093	$ 448	792,689	(4,717,962)	4,720,523	(345,605)
Ending balance, shares at Jun. 30, 2020		23,971,265
Beginning balance at Dec. 31, 2020	$ 282,675	$ 448	805,140	(5,283,584)	5,095,596	(334,925)
Beginning balance, shares at Dec. 31, 2020	24,125,317	23,471,841
Stock Issued During Period, Value, Treasury Stock Reissued	$ (5,049)		(1,239)	(4,682)	(872)
Exercise of stock options and restricted stock units, shares		22,388
Treasury Stock, Value, Acquired, Cost Method	(262,500)			(262,500)
Repurchases of common stock, shares		(224,808)
Adjustment to Additional Paid in Capital, Share-Based Compensation	4,575		4,575
Net earnings	149,663				149,663
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	23,181					23,181
Ending balance at Mar. 31, 2021	202,643	$ 448	810,954	(5,541,402)	5,244,387	(311,744)
Ending balance, shares at Mar. 31, 2021		23,269,421
Beginning balance at Dec. 31, 2020	$ 282,675	$ 448	805,140	(5,283,584)	5,095,596	(334,925)
Beginning balance, shares at Dec. 31, 2020	24,125,317	23,471,841
Exercise of stock options and restricted stock units, shares	35,636
Treasury Stock, Value, Acquired, Cost Method	$ (475,000)
Repurchases of common stock, shares	(390,538)
Net earnings	$ 334,426
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	32,333
Ending balance at Jun. 30, 2021	$ 191,424	$ 448	815,535	(5,751,052)	5,429,085	(302,592)
Ending balance, shares at Jun. 30, 2021	23,794,563	23,116,939
Beginning balance at Mar. 31, 2021	$ 202,643	$ 448	810,954	(5,541,402)	5,244,387	(311,744)
Beginning balance, shares at Mar. 31, 2021		23,269,421
Stock Issued During Period, Value, Treasury Stock Reissued	(2,784)		0	(2,849)	(65)
Exercise of stock options and restricted stock units, shares		13,248
Treasury Stock, Value, Acquired, Cost Method	(212,499)			(212,499)
Repurchases of common stock, shares		(165,730)
Adjustment to Additional Paid in Capital, Share-Based Compensation	4,581		4,581
Net earnings	184,763				184,763
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	9,152					9,152
Ending balance at Jun. 30, 2021	$ 191,424	$ 448	$ 815,535	$ (5,751,052)	$ 5,429,085	$ (302,592)
Ending balance, shares at Jun. 30, 2021	23,794,563	23,116,939