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, 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	17,723			17,723
Stock options exercised, shares		136,740
Stock options exercised	2,428		(550)		2,978
Stock-based compensation expense	912		912
Repurchase of common shares, shares		(201,088)
Repurchase of common shares	(5,150)				(5,150)
Deferral of executive and director compensation	246		246
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 Mar. 31, 2019		27,568,826
Stockholders' Equity, Ending Balance at Mar. 31, 2019	871,462	$ 301	328,580	598,715	(56,134)
Shares Outstanding, Beginning Balance at Dec. 31, 2019		28,386,456
Stockholders' Equity, Beginning Balance at Dec. 31, 2019	1,003,477	$ 301	332,861	708,579	(38,264)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	31,746			31,746
Stock options exercised, shares		132,300
Stock options exercised	3,182		290		2,892
Stock-based compensation expense	$ 973		973
Repurchase of common shares, shares	100,000	(80,000)
Repurchase of common shares	$ (1,912)				(1,912)
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 Mar. 31, 2020		28,523,329
Stockholders' Equity, Ending Balance at Mar. 31, 2020	$ 1,037,681	$ 301	$ 332,490	$ 740,325	$ (35,435)