CONSOLIDATED STATEMENT OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]	Treasury Stock, Common [Member]	Series A Nonconvertible Preferred Stock [Member] Preferred Stock [Member]
BALANCE at Dec. 31, 2020	$ 912,714	$ 490	$ 635,595	$ 353,930	$ (36,019)	$ (41,284)	$ 2
BALANCE (in shares) at Dec. 31, 2020		49,013,476				1,365,648	200,000
Net income	184,213			184,213
Other comprehensive income (loss)	17,784				17,784
Cash dividend	(37,931)			(37,931)
Issuance of common stock to employees	34,472	$ 1	34,471
Issuance of common stock to employees (in shares)		63,969
Shares withheld for employee taxes	(14,949)		(14,949)
Shares withheld for employee taxes (in shares)		(29,179)
Issuance of common stock to Board of Directors and Scientific Advisory Board	1,704		1,704
Issuance of common stock to Board of Directors and Scientific Advisory Board (in shares)		8,502
Issuance of common stock to employees under an ESPP	1,907		1,907
Issuance of common stock to employees under an ESPP (in shares)		9,156
BALANCE at Dec. 31, 2021	1,099,914	$ 491	658,728	500,212	(18,235)	$ (41,284)	$ 2
BALANCE (in shares) at Dec. 31, 2021		49,065,924				1,365,648	200,000
Net income	210,061			210,061
Other comprehensive income (loss)	(217)				(217)
Cash dividend	(56,996)			(56,996)
Issuance of common stock to employees	27,907		27,907
Issuance of common stock to employees (in shares)		72,769
Shares withheld for employee taxes	$ (9,209)		(9,209)
Shares withheld for employee taxes (in shares)		(31,938)
Common shares repurchased (in shares)	0
Issuance of common stock to Board of Directors and Scientific Advisory Board	$ 1,866		1,866
Issuance of common stock to Board of Directors and Scientific Advisory Board (in shares)		12,218
Issuance of common stock to employees under an ESPP	2,043		2,043
Issuance of common stock to employees under an ESPP (in shares)		17,057
BALANCE at Dec. 31, 2022	1,275,369	$ 491	681,335	653,277	(18,452)	$ (41,284)	$ 2
BALANCE (in shares) at Dec. 31, 2022		49,136,030				1,365,648	200,000
Net income	203,011			203,011
Other comprehensive income (loss)	17,366				17,366
Cash dividend	(66,735)			(66,735)
Issuance of common stock to employees	21,793	$ 1	21,792
Issuance of common stock to employees (in shares)		145,428
Shares withheld for employee taxes	$ (8,206)	$ 0	(8,206)
Shares withheld for employee taxes (in shares)		(58,512)
Common shares repurchased (in shares)	0
Issuance of common stock to Board of Directors and Scientific Advisory Board	$ 2,074		2,074
Issuance of common stock to Board of Directors and Scientific Advisory Board (in shares)		16,808
Issuance of common stock to employees under an ESPP	2,554		2,554
Issuance of common stock to employees under an ESPP (in shares)		17,513
Shares Issued, Shares, Share-Based Payment Arrangement, Forfeited		(526,241)
Stock Issued During Period, Value, Restricted Stock Award, Forfeitures	0	$ (5)	5
BALANCE at Dec. 31, 2023	$ 1,447,226	$ 487	$ 699,554	$ 789,553	$ (1,086)	$ (41,284)	$ 2
BALANCE (in shares) at Dec. 31, 2023		48,731,026				1,365,648	200,000