Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Earnings (Deficit) [Member]
BALANCE at Dec. 31, 2019	$ 431,295	$ 860	$ (227,315)	$ 639,335	$ 344	$ 18,071
BALANCE, shares at Dec. 31, 2019		85,953,000
BALANCE, shares at Dec. 31, 2019			(15,802,000)
NET INCOME	124,264					124,264
Foreign currency translation	199				199
Unrealized gain (loss) on investments	(179)				(179)
COMPREHENSIVE INCOME	124,284
Treasury stock purchased	(17,862)		$ (17,862)
Treasury stock purchased, shares			(1,320,000)
Share-based compensation expense:
Stock option plans	1,134			1,134
Restricted stock award plans	12,227			12,227
Employee stock purchase plan	18			18
Common stock issued under:
Stock option plans	$ 5,384	$ 10		5,374
Stock option plan, shares	1,040,304	1,040,000
Restricted stock award plans	$ (912)	$ 2	$ (911)	(3)
Restricted stock award plan, shares		243,000	(81,000)
Employee stock purchase plan	339	$ 1		338
Employee stock purchase plan, shares		29,000
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	88,724,438	88,724,000
BALANCE, shares at Dec. 31, 2021	(19,975,776)		(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)