Condensed Consolidated Statement of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Shares [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Treasury Stock, Common
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	360,267			360,267
Stock options exercised, shares		38,800
Stock options exercised	1,002		(687)		1,689
Stock-based compensation expense	6,613		6,613
Repurchase of common shares, shares		(1,200,000)
Repurchase of common shares	(55,334)				(55,334)
Deferral of executive and director compensation	1,041		1,041
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 Sep. 30, 2022		27,428,983
Stockholders' Equity, Ending Balance at Sep. 30, 2022	1,937,773	$ 301	350,569	1,705,588	(118,685)
Shares Outstanding, Beginning Balance at Jun. 30, 2022		27,760,583
Stockholders' Equity, Beginning Balance at Jun. 30, 2022	1,818,267	$ 301	347,923	1,573,998	(103,955)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	131,590			131,590
Stock options exercised, shares		8,400
Stock options exercised	232		(137)		369
Stock-based compensation expense	2,764		2,764
Repurchase of common shares, shares		(340,000)
Repurchase of common shares	(15,099)				(15,099)
Deferral of executive and director compensation			19
Shares Outstanding, Ending Balance at Sep. 30, 2022		27,428,983
Stockholders' Equity, Ending Balance at Sep. 30, 2022	1,937,773	$ 301	350,569	1,705,588	(118,685)
Shares Outstanding, Beginning Balance at Dec. 31, 2022		27,440,083
Stockholders' Equity, Beginning Balance at Dec. 31, 2022	2,070,725	$ 301	352,639	1,835,983	(118,198)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	360,083			360,083
Stock options exercised, shares		778,358
Stock options exercised	27,152		(7,858)		35,010
Stock-based compensation expense	7,006		7,006
Repurchase of common shares, shares		(473,000)
Repurchase of common shares	(40,259)				(40,259)
Deferral of executive and director compensation	1,005		1,005
Deferred Compensation Arrangement with Individual, Shares Issued		103,081
Deferred Compensation Arrangement with Individual, Distribution Paid	0		(4,630)		4,630
Shares Outstanding, Ending Balance at Sep. 30, 2023		27,848,522
Stockholders' Equity, Ending Balance at Sep. 30, 2023	2,425,712	$ 301	348,162	2,196,066	(118,817)
Shares Outstanding, Beginning Balance at Jun. 30, 2023		27,782,616
Stockholders' Equity, Beginning Balance at Jun. 30, 2023	2,298,459	$ 301	350,127	2,057,050	(109,019)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	139,016			139,016
Stock options exercised, shares		283,292
Stock options exercised	10,583		(2,559)		13,142
Stock-based compensation expense	$ 2,682		2,682
Repurchase of common shares, shares	300,000	(263,000)
Repurchase of common shares	$ (25,052)				(25,052)
Deferral of executive and director compensation	24		24
Deferred Compensation Arrangement with Individual, Shares Issued		45,614
Deferred Compensation Arrangement with Individual, Distribution Paid	0		(2,112)		2,112
Shares Outstanding, Ending Balance at Sep. 30, 2023		27,848,522
Stockholders' Equity, Ending Balance at Sep. 30, 2023	$ 2,425,712	$ 301	$ 348,162	$ 2,196,066	$ (118,817)