Condensed Consolidated Statement of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Shares [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Treasury Shares [Member]
Shares Outstanding, Beginning Balance at Dec. 31, 2020		28,813,849
Stockholders' Equity, Beginning Balance at Dec. 31, 2020	$ 1,258,698	$ 301	$ 339,001	$ 948,453	$ (29,057)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	192,473			192,473
Stock options exercised, shares		428,100
Stock options exercised	10,630		1,230		9,400
Stock-based compensation expense	4,405		4,405
Deferral of executive and director compensation	338		338
Deferred Compensation Arrangement with Individual, Shares Issued		76,181
Deferred Compensation Arrangement with Individual, Distribution Paid	0		(1,673)		1,673
Shares Outstanding, Ending Balance at Jun. 30, 2021		29,318,130
Stockholders' Equity, Ending Balance at Jun. 30, 2021	1,466,544	$ 301	343,301	1,140,926	(17,984)
Shares Outstanding, Beginning Balance at Mar. 31, 2021		29,185,630
Stockholders' Equity, Beginning Balance at Mar. 31, 2021	1,353,422	$ 301	340,696	1,033,319	(20,894)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	107,607			107,607
Stock options exercised, shares		132,500
Stock options exercised	3,374		464		2,910
Stock-based compensation expense	2,141		2,141
Shares Outstanding, Ending Balance at Jun. 30, 2021		29,318,130
Stockholders' Equity, Ending Balance at Jun. 30, 2021	1,466,544	$ 301	343,301	1,140,926	(17,984)
Shares Outstanding, Beginning Balance at Dec. 31, 2021		28,499,630
Stockholders' Equity, Beginning Balance at Dec. 31, 2021	1,624,184	$ 301	347,452	1,345,321	(68,890)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	228,677			228,677
Stock options exercised, shares		30,400
Stock options exercised	770		(550)		1,320
Stock-based compensation expense	3,849		3,849
Repurchase of common shares, shares		(860,000)
Repurchase of common shares	(40,235)				(40,235)
Deferral of executive and director compensation	1,022		1,022
Deferred Compensation Arrangement with Individual, Shares Issued		90,553
Deferred Compensation Arrangement with Individual, Distribution Paid	0		(3,850)		3,850
Shares Outstanding, Ending Balance at Jun. 30, 2022		27,760,583
Stockholders' Equity, Ending Balance at Jun. 30, 2022	1,818,267	$ 301	347,923	1,573,998	(103,955)
Shares Outstanding, Beginning Balance at Mar. 31, 2022		28,288,783
Stockholders' Equity, Beginning Balance at Mar. 31, 2022	1,703,689	$ 301	346,291	1,437,160	(80,063)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	136,838			136,838
Stock options exercised, shares		21,800
Stock options exercised	564		(386)		950
Stock-based compensation expense	$ 2,018		2,018
Repurchase of common shares, shares	600,000	(550,000)
Repurchase of common shares	$ (24,842)				(24,842)
Shares Outstanding, Ending Balance at Jun. 30, 2022		27,760,583
Stockholders' Equity, Ending Balance at Jun. 30, 2022	$ 1,818,267	$ 301	$ 347,923	$ 1,573,998	$ (103,955)