Statement of Stockholders' Equity - USD ($) $ in Thousands	Total		Common Stock	Additional Paid-In Capital	Treasury Stock	Retained Earnings
Beginning balance (in shares) at Dec. 31, 2018			26,907,000		6,027,000
Beginning balance at Dec. 31, 2018	$ 720,456		$ 269	$ 60,822	$ (91,056)	$ 750,421
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	13,411					13,411
Stock-based compensation	760			760
Exercise of stock options (in shares)			15,000
Exercise of stock options	431			431
Dividends declared	(418)					(418)
Beginning balance (in shares) at Mar. 31, 2019			26,922,000		6,027,000
Beginning balance at Mar. 31, 2019	734,640		$ 269	62,013	$ (91,056)	763,414
Beginning balance (in shares) at Dec. 31, 2018			26,907,000		6,027,000
Beginning balance at Dec. 31, 2018	720,456		$ 269	60,822	$ (91,056)	750,421
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 31,193
Purchase of treasury stock (in shares)	0
Beginning balance (in shares) at Jun. 30, 2019			26,933,000		6,027,000
Beginning balance at Jun. 30, 2019	$ 752,643		$ 269	62,652	$ (91,056)	780,778
Beginning balance (in shares) at Mar. 31, 2019			26,922,000		6,027,000
Beginning balance at Mar. 31, 2019	734,640		$ 269	62,013	$ (91,056)	763,414
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	17,782					17,782
Stock-based compensation (in shares)			5,000
Stock-based compensation	502			502
Exercise of stock options (in shares)			6,000
Exercise of stock options	137			137
Dividends declared	(418)					(418)
Beginning balance (in shares) at Jun. 30, 2019			26,933,000		6,027,000
Beginning balance at Jun. 30, 2019	752,643		$ 269	62,652	$ (91,056)	780,778
Beginning balance (in shares) at Dec. 31, 2019			26,939,000		6,027,000
Beginning balance at Dec. 31, 2019	779,096	[1]	$ 269	63,009	$ (91,056)	806,874
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	18,607					18,607
Stock-based compensation (in shares)			8,000
Stock-based compensation	460			460
Dividends declared	(411)					(411)
Purchase of treasury stock (in shares)					439,000
Purchase of treasury stock	(20,580)				$ (20,580)
Beginning balance (in shares) at Mar. 31, 2020			26,947,000		6,466,000
Beginning balance at Mar. 31, 2020	777,172		$ 269	63,469	$ (111,636)	825,070
Beginning balance (in shares) at Dec. 31, 2019			26,939,000		6,027,000
Beginning balance at Dec. 31, 2019	779,096	[1]	$ 269	63,009	$ (91,056)	806,874
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 30,955
Purchase of treasury stock (in shares)	441,250
Beginning balance (in shares) at Jun. 30, 2020			27,005,000		6,468,000
Beginning balance at Jun. 30, 2020	$ 792,111		$ 270	66,554	$ (111,718)	837,005
Beginning balance (in shares) at Mar. 31, 2020			26,947,000		6,466,000
Beginning balance at Mar. 31, 2020	777,172		$ 269	63,469	$ (111,636)	825,070
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	12,347					12,347
Stock-based compensation (in shares)			5,000
Stock-based compensation	631			631
Exercise of stock options (in shares)			53,000
Exercise of stock options	2,455		$ 1	2,454
Dividends declared	(412)					(412)
Purchase of treasury stock (in shares)					2,000
Purchase of treasury stock	(82)				$ (82)
Beginning balance (in shares) at Jun. 30, 2020			27,005,000		6,468,000
Beginning balance at Jun. 30, 2020	$ 792,111		$ 270	$ 66,554	$ (111,718)	$ 837,005

[1] The balance sheet at December 31, 2019, as presented, is derived from the audited financial statements at that date.