CONSOLIDATED STATEMENTS OF STOCKHOLDERS EQUITY - USD ($) shares in Thousands, $ in Thousands	Common Stock	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Loss	Total
Balance at Dec. 31, 2021	$ 722,310	$ 2,163,916	$ (618,712)		$ 2,267,514
Balance (in shares) at Dec. 31, 2021	82,336		(31,956)
Increase (Decrease) in Stockholders' Equity
Net Income (loss)		17,734			17,734
Exercise of common stock options and vested employee stock awards	$ 27				27
Exercise of common stock options and vested employee stock awards (in shares)	139
Employee income tax paid on vested equity awards			$ (1,123)		(1,123)
Employee income tax paid on vested equity awards (in shares)			(37)
Sale of common stock under employee stock purchase plan	$ 1,487				1,487
Sale of common stock under employee stock purchase plan (in shares)	40
Stock based compensation expense	$ 4,076				4,076
Balance at Mar. 31, 2022	$ 727,900	2,181,650	$ (619,835)		2,289,715
Balance (in shares) at Mar. 31, 2022	82,515		(31,993)
Balance at Dec. 31, 2021	$ 722,310	2,163,916	$ (618,712)		2,267,514
Balance (in shares) at Dec. 31, 2021	82,336		(31,956)
Increase (Decrease) in Stockholders' Equity
Net Income (loss)					120,057
Net unrealized appreciation (depreciation) on marketable securities, net of tax					(4,569)
Balance at Sep. 30, 2022	$ 736,406	2,283,973	$ (619,862)	$ (4,569)	2,395,948
Balance (in shares) at Sep. 30, 2022	82,592		(31,994)
Balance at Mar. 31, 2022	$ 727,900	2,181,650	$ (619,835)		2,289,715
Balance (in shares) at Mar. 31, 2022	82,515		(31,993)
Increase (Decrease) in Stockholders' Equity
Net Income (loss)		53,951			53,951
Stock based compensation expense	$ 3,310				3,310
Net unrealized appreciation (depreciation) on marketable securities, net of tax				(1,945)	(1,945)
Balance at Jun. 30, 2022	$ 731,210	2,235,601	$ (619,835)	(1,945)	2,345,031
Balance (in shares) at Jun. 30, 2022	82,515		(31,993)
Increase (Decrease) in Stockholders' Equity
Net Income (loss)		48,372			48,372
Exercise of common stock options and vested employee stock awards	$ 115				115
Exercise of common stock options and vested employee stock awards (in shares)	11
Employee income tax paid on vested equity awards			$ (27)		(27)
Employee income tax paid on vested equity awards (in shares)			(1)
Sale of common stock under employee stock purchase plan	$ 1,329				1,329
Sale of common stock under employee stock purchase plan (in shares)	66
Stock based compensation expense	$ 3,752				3,752
Net unrealized appreciation (depreciation) on marketable securities, net of tax				(2,624)	(2,624)
Balance at Sep. 30, 2022	$ 736,406	2,283,973	$ (619,862)	(4,569)	2,395,948
Balance (in shares) at Sep. 30, 2022	82,592		(31,994)
Balance at Dec. 31, 2022	$ 734,426	2,236,869	$ (619,862)	(3,802)	2,347,631
Balance (in shares) at Dec. 31, 2022	82,593		(31,994)
Increase (Decrease) in Stockholders' Equity
Net Income (loss)		(22,071)			(22,071)
Exercise of common stock options and vested employee stock awards	$ 57				57
Exercise of common stock options and vested employee stock awards (in shares)	130
Employee income tax paid on vested equity awards			$ (585)		(585)
Employee income tax paid on vested equity awards (in shares)			(32)
Sale of common stock under employee stock purchase plan	$ 1,218				1,218
Sale of common stock under employee stock purchase plan (in shares)	78
Stock based compensation expense	$ 4,329				4,329
Treasury stock purchases			$ (100,001)		(100,001)
Treasury stock purchases (in shares)			(5,067)
Net unrealized appreciation (depreciation) on marketable securities, net of tax				1,480	1,480
Balance at Mar. 31, 2023	$ 740,030	2,214,798	$ (720,448)	(2,322)	2,232,058
Balance (in shares) at Mar. 31, 2023	82,801		(37,093)
Balance at Dec. 31, 2022	$ 734,426	2,236,869	$ (619,862)	(3,802)	2,347,631
Balance (in shares) at Dec. 31, 2022	82,593		(31,994)
Increase (Decrease) in Stockholders' Equity
Net Income (loss)					16,826
Net unrealized appreciation (depreciation) on marketable securities, net of tax					3,618
Balance at Sep. 30, 2023	$ 750,133	2,253,695	$ (866,946)	(184)	2,136,698
Balance (in shares) at Sep. 30, 2023	82,840		(41,620)
Balance at Mar. 31, 2023	$ 740,030	2,214,798	$ (720,448)	(2,322)	2,232,058
Balance (in shares) at Mar. 31, 2023	82,801		(37,093)
Increase (Decrease) in Stockholders' Equity
Net Income (loss)		15,419			15,419
Stock based compensation expense	$ 4,246				4,246
Treasury stock purchases			$ (95,998)		(95,998)
Treasury stock purchases (in shares)			(3,335)
Net unrealized appreciation (depreciation) on marketable securities, net of tax				1,514	1,514
Balance at Jun. 30, 2023	$ 744,276	2,230,217	$ (816,446)	(808)	2,157,239
Balance (in shares) at Jun. 30, 2023	82,801		(40,428)
Increase (Decrease) in Stockholders' Equity
Net Income (loss)		23,478			23,478
Sale of common stock under employee stock purchase plan	$ 1,536				1,536
Sale of common stock under employee stock purchase plan (in shares)	39
Stock based compensation expense	$ 4,321				4,321
Treasury stock purchases			$ (50,500)		(50,500)
Treasury stock purchases (in shares)			(1,192)
Net unrealized appreciation (depreciation) on marketable securities, net of tax				624	624
Balance at Sep. 30, 2023	$ 750,133	$ 2,253,695	$ (866,946)	$ (184)	$ 2,136,698
Balance (in shares) at Sep. 30, 2023	82,840		(41,620)