Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive (Loss) Income [Member]	Retained Earnings [Member]
BALANCE at Dec. 31, 2020	$ 555,907	$ 873	$ (246,088)	$ 658,423	$ 364	$ 142,335
BALANCE, shares at Dec. 31, 2020		87,265,000
BALANCE, shares at Dec. 31, 2020			(17,203,000)
NET INCOME	109,637					109,637
Foreign currency translation	(177)				(177)
Unrealized gain (loss) on investments	(283)				(283)
COMPREHENSIVE INCOME	109,177
Treasury stock purchased	(25,296)		$ (25,296)
Treasury stock purchased, shares			(2,313,000)
Share-based compensation expense:
Stock option plans	464			464
Restricted stock award plans	14,495			14,495
Employee stock purchase plan	13			13
Common stock issued under:
Stock option plans	$ 549	$ 1		548
Stock option plan, shares	103,407	103,000
Restricted stock award plans	$ (5,511)	$ 13	$ (5,511)	(13)
Restricted stock award plan, shares		1,329,000	(460,000)
Employee stock purchase plan	312			312
Employee stock purchase plan, shares		27,000
BALANCE at Dec. 31, 2021	650,110	$ 887	$ (276,895)	674,242	(96)	251,972
BALANCE, shares at Dec. 31, 2021		88,724,000
BALANCE, shares at Dec. 31, 2021			(19,976,000)
NET INCOME	95,867					95,867
Foreign currency translation	(166)				(166)
Unrealized gain (loss) on investments	(5,185)				(5,185)
COMPREHENSIVE INCOME	90,516
Treasury stock purchased	(23,117)		$ (23,117)
Treasury stock purchased, shares			(2,099,000)
Share-based compensation expense:
Stock option plans	89			89
Restricted stock award plans	8,648			8,648
Employee stock purchase plan	14			14
Common stock issued under:
Stock option plans	$ 930	$ 1		929
Stock option plan, shares	144,009	144,000
Restricted stock award plans	$ (1,612)	$ 6	$ (1,612)	(6)
Restricted stock award plan, shares		504,000	(146,000)
Employee stock purchase plan	267			267
Employee stock purchase plan, shares		24,000
BALANCE at Dec. 31, 2022	$ 725,845	$ 894	$ (301,624)	684,183	(5,447)	347,839
BALANCE, shares at Dec. 31, 2022	89,396,192	89,396,000
BALANCE, shares at Dec. 31, 2022	(22,220,707)		(22,221,000)
NET INCOME	$ 147,652					147,652
Foreign currency translation	45				45
Unrealized gain (loss) on investments	4,736				4,736
COMPREHENSIVE INCOME	152,433
Dividends to shareholders, per share $0.22	(14,885)					(14,885)
Treasury stock purchased	(8,301)		$ (8,301)
Treasury stock purchased, shares			(540,000)
Treasury stock acquired upon sale of asset, shares			(1,800,000)
Treasury stock acquired upon sale of asset	(22,086)		$ (22,086)
Share-based compensation expense:
Restricted stock award plans	8,064			8,064
Employee stock purchase plan	14			14
Common stock issued under:
Stock option plans	$ 2,279	$ 3		2,276
Stock option plan, shares	309,819	310,000
Restricted stock award plans	$ (2,208)	$ 6	$ (2,209)	(5)
Restricted stock award plan, shares		545,000	(165,000)
Employee stock purchase plan	266			266
Employee stock purchase plan, shares		19,000
BALANCE at Dec. 31, 2023	$ 841,421	$ 903	$ (334,220)	$ 694,798	$ (666)	$ 480,606
BALANCE, shares at Dec. 31, 2023	90,270,306	90,270,000
BALANCE, shares at Dec. 31, 2023	(24,725,767)		(24,726,000)