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	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		(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)
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	221,067			221,067
Stock options exercised, shares		495,066
Stock options exercised	16,569		(5,299)		21,868
Stock-based compensation expense	4,324		4,324
Repurchase of common shares, shares		(210,000)
Repurchase of common shares	(15,207)				(15,207)
Deferral of executive and director compensation	981		981
Deferred Compensation Arrangement with Individual, Shares Issued		57,467
Deferred Compensation Arrangement with Individual, Distribution Paid	0		(2,518)		2,518
Shares Outstanding, Ending Balance at Jun. 30, 2023		27,782,616
Stockholders' Equity, Ending Balance at Jun. 30, 2023	2,298,459	$ 301	350,127	2,057,050	(109,019)
Shares Outstanding, Beginning Balance at Mar. 31, 2023		27,715,616
Stockholders' Equity, Beginning Balance at Mar. 31, 2023	2,183,215	$ 301	349,988	1,939,049	(106,123)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	118,001			118,001
Stock options exercised, shares		277,000
Stock options exercised	10,130		(2,181)		12,311
Stock-based compensation expense	$ 2,301		2,301
Repurchase of common shares, shares	200,000	(210,000)
Repurchase of common shares	$ (15,207)				(15,207)
Deferral of executive and director compensation	19		19
Shares Outstanding, Ending Balance at Jun. 30, 2023		27,782,616
Stockholders' Equity, Ending Balance at Jun. 30, 2023	$ 2,298,459	$ 301	$ 350,127	$ 2,057,050	$ (109,019)