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, 2018		27,516,218
Stockholders' Equity, Beginning Balance at Dec. 31, 2018	$ 855,303	$ 301	$ 330,517	$ 580,992	$ (56,507)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	127,587			127,587
Treasury Stock, Shares, Acquired		(201,088)
Treasury Stock, Value, Acquired, Cost Method	(5,150)				(5,150)
Stock options exercised - shares		954,370
Stock options exercised - value	19,644		(1,204)		20,848
Stock-based compensation expense	5,846		5,846
Deferral of Executive and Director Compensation	247		247
Deferred Compensation Arrangement with Individual, Shares Issued		116,956
Deferred Compensation Arrangement with Individual, Distribution Paid	0		(2,545)		2,545
Shares Outstanding, Ending Balance at Dec. 31, 2019		28,386,456
Stockholders' Equity, Ending Balance at Dec. 31, 2019	1,003,477	$ 301	332,861	708,579	(38,264)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	239,874			239,874
Treasury Stock, Shares, Acquired		(80,000)
Treasury Stock, Value, Acquired, Cost Method	(1,912)				(1,912)
Stock options exercised - shares		422,820
Stock options exercised - value	9,906		636		9,270
Stock-based compensation expense	7,138		7,138
Deferral of Executive and Director Compensation	215		215
Deferred Compensation Arrangement with Individual, Shares Issued		84,573
Deferred Compensation Arrangement with Individual, Distribution Paid	0		(1,849)		1,849
Shares Outstanding, Ending Balance at Dec. 31, 2020		28,813,849
Stockholders' Equity, Ending Balance at Dec. 31, 2020	1,258,698	$ 301	339,001	948,453	(29,057)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 396,868			396,868
Treasury Stock, Shares, Acquired	800,000	(842,500)
Treasury Stock, Value, Acquired, Cost Method	$ (51,520)				(51,520)
Stock options exercised - shares	452,100	452,100
Stock options exercised - value	$ 11,241		1,227		10,014
Stock-based compensation expense	8,559		8,559
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 Dec. 31, 2021		28,499,630
Stockholders' Equity, Ending Balance at Dec. 31, 2021	$ 1,624,184	$ 301	$ 347,452	$ 1,345,321	$ (68,890)