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, 2020	$ 704,675	$ 2,052,006	$ (617,136)		$ 2,139,545
Balance (in shares) at Dec. 31, 2020	82,095		(31,914)
Increase (Decrease) in Stockholders' Equity
Net income		35,900			35,900
Exercise of common stock options and vested employee stock awards	$ 606				606
Exercise of common stock options and vested employee stock awards (in shares)	177
Employee income tax paid on vested equity awards			$ (1,573)		(1,573)
Employee income tax paid on vested equity awards (in shares)			(42)
Sale of common stock under employee stock purchase plan	$ 1,139				1,139
Sale of common stock under employee stock purchase plan (in shares)	30
Stock based compensation expense	$ 2,613				2,613
Warrants issued to U.S. Treasury	3,291				3,291
Balance at Mar. 31, 2021	$ 712,324	2,087,906	$ (618,709)		2,181,521
Balance (in shares) at Mar. 31, 2021	82,302		(31,956)
Balance at Dec. 31, 2020	$ 704,675	2,052,006	$ (617,136)		2,139,545
Balance (in shares) at Dec. 31, 2020	82,095		(31,914)
Increase (Decrease) in Stockholders' Equity
Net income					107,578
Balance at Sep. 30, 2021	$ 720,932	2,159,584	$ (618,709)		2,261,807
Balance (in shares) at Sep. 30, 2021	82,336		(31,956)
Balance at Mar. 31, 2021	$ 712,324	2,087,906	$ (618,709)		2,181,521
Balance (in shares) at Mar. 31, 2021	82,302		(31,956)
Increase (Decrease) in Stockholders' Equity
Net income		61,994			61,994
Stock based compensation expense	$ 2,877				2,877
Warrants issued to U.S. Treasury	2,513				2,513
Balance at Jun. 30, 2021	$ 717,714	2,149,900	$ (618,709)		2,248,905
Balance (in shares) at Jun. 30, 2021	82,302		(31,956)
Increase (Decrease) in Stockholders' Equity
Net income		9,684			9,684
Sale of common stock under employee stock purchase plan	$ 1,401				1,401
Sale of common stock under employee stock purchase plan (in shares)	34
Stock based compensation expense	$ 1,817				1,817
Balance at Sep. 30, 2021	$ 720,932	2,159,584	$ (618,709)		2,261,807
Balance (in shares) at Sep. 30, 2021	82,336		(31,956)
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		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					120,057
Net unrealized 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		53,951			53,951
Stock based compensation expense	$ 3,310				3,310
Net unrealized 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		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 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)