CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]	Treasury Stock [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	92,228			92,228
Other comprehensive loss	2,247				2,247
Cash dividend	(18,970)			(18,970)
Issuance of common stock to employees	14,412	$ 1	14,411
Issuance of common stock to employees (in shares)		57,390
Shares withheld for employee taxes	(13,018)		(13,018)
Shares withheld for employee taxes (in shares)		(26,708)
Issuance of common stock to Board of Directors and Scientific Advisory Board	1,004		1,004
Issuance of common stock to Board of Directors and Scientific Advisory Board (in shares)		5,796
Issuance of common stock to employees under an ESPP	999		999
Issuance of common stock to employees under an ESPP (in shares)		4,105
BALANCE at Jun. 30, 2021	991,616	$ 491	638,991	427,188	(33,772)	$ (41,284)	$ 2
BALANCE (in shares) at Jun. 30, 2021		49,054,059				1,365,648	200,000
BALANCE at Mar. 31, 2021	952,468	$ 491	632,138	396,130	(35,009)	$ (41,284)	$ 2
BALANCE (in shares) at Mar. 31, 2021		49,050,776				1,365,648	200,000
Net income	40,541			40,541
Other comprehensive loss	1,237				1,237
Cash dividend	(9,483)			(9,483)
Issuance of common stock to employees	9,296		9,296
Issuance of common stock to employees (in shares)		4,267
Shares withheld for employee taxes	(3,384)		(3,384)
Shares withheld for employee taxes (in shares)		(4,660)
Issuance of common stock to Board of Directors and Scientific Advisory Board	374		374
Issuance of common stock to Board of Directors and Scientific Advisory Board (in shares)		1,353
Issuance of common stock to employees under an ESPP	567		567
Issuance of common stock to employees under an ESPP (in shares)		2,323
BALANCE at Jun. 30, 2021	991,616	$ 491	638,991	427,188	(33,772)	$ (41,284)	$ 2
BALANCE (in shares) at Jun. 30, 2021		49,054,059				1,365,648	200,000
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	91,472			91,472
Other comprehensive loss	(4,943)				(4,943)
Cash dividend	(28,493)			(28,493)
Issuance of common stock to employees	13,938		13,938
Issuance of common stock to employees (in shares)		62,134
Shares withheld for employee taxes	(8,844)		(8,844)
Shares withheld for employee taxes (in shares)		(28,482)
Issuance of common stock to Board of Directors and Scientific Advisory Board	1,074		1,074
Issuance of common stock to Board of Directors and Scientific Advisory Board (in shares)		7,826
Issuance of common stock to employees under an ESPP	1,191		1,191
Issuance of common stock to employees under an ESPP (in shares)		8,042
BALANCE at Jun. 30, 2022	1,165,309	$ 491	666,087	563,191	(23,178)	$ (41,284)	$ 2
BALANCE (in shares) at Jun. 30, 2022		49,115,444				1,365,648	200,000
BALANCE at Mar. 31, 2022	1,131,300	$ 491	658,050	535,936	(21,895)	$ (41,284)	$ 2
BALANCE (in shares) at Mar. 31, 2022		49,099,830				1,365,648	200,000
Net income	41,502			41,502
Other comprehensive loss	(1,283)				(1,283)
Cash dividend	(14,247)			(14,247)
Issuance of common stock to employees	7,959		7,959
Issuance of common stock to employees (in shares)		14,386
Shares withheld for employee taxes	(948)		(948)
Shares withheld for employee taxes (in shares)		(6,135)
Issuance of common stock to Board of Directors and Scientific Advisory Board	344		344
Issuance of common stock to Board of Directors and Scientific Advisory Board (in shares)		2,196
Issuance of common stock to employees under an ESPP	682		682
Issuance of common stock to employees under an ESPP (in shares)		5,167
BALANCE at Jun. 30, 2022	$ 1,165,309	$ 491	$ 666,087	$ 563,191	$ (23,178)	$ (41,284)	$ 2
BALANCE (in shares) at Jun. 30, 2022		49,115,444				1,365,648	200,000