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					97,894
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)
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)
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					71,685
Net unrealized depreciation on marketable securities, net of tax of $628					(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)
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 of $628				(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)