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, 2019	$ 811,449	$ 489	$ 620,236	$ 249,003	$ (16,997)	$ (41,284)	$ 2
BALANCE (in shares) at Dec. 31, 2019		48,852,193				1,365,648	200,000
Net Income Loss	79,470			79,470
Other comprehensive income (loss)	2,230				2,230
Cash dividend	(21,329)			(21,329)
Issuance of common stock to employees	19,534	$ 2	19,532
Issuance of common stock to employees (in shares)		238,996
Shares withheld for employee taxes	(14,293)	$ (1)	(14,292)
Shares withheld for employee taxes (in shares)		(98,882)
Issuance of common stock to Board of Directors and Scientific Advisory Board	1,433		1,433
Issuance of common stock to Board of Directors and Scientific Advisory Board (in shares)		8,906
Issuance of common stock to employees under an ESPP	1,142		1,142
Issuance of common stock to employees under an ESPP (in shares)		7,702
BALANCE at Sep. 30, 2020	$ 879,636	$ 490	628,051	307,144	(14,767)	$ (41,284)	$ 2
BALANCE (in shares) at Sep. 30, 2020	49,008,915	49,008,915				1,365,648	200,000
BALANCE at Jun. 30, 2020	$ 839,770	$ 490	621,585	273,758	(14,781)	$ (41,284)	$ 2
BALANCE (in shares) at Jun. 30, 2020		48,992,532				1,365,648	200,000
Net Income Loss	40,500			40,500
Other comprehensive income (loss)	14				14
Cash dividend	(7,114)			(7,114)
Issuance of common stock to employees	6,805	$ 1	6,804
Issuance of common stock to employees (in shares)		19,733
Shares withheld for employee taxes	(1,128)	$ (1)	(1,127)
Shares withheld for employee taxes (in shares)		(7,199)
Issuance of common stock to Board of Directors and Scientific Advisory Board	425		425
Issuance of common stock to Board of Directors and Scientific Advisory Board (in shares)		1,614
Issuance of common stock to employees under an ESPP	364		364
Issuance of common stock to employees under an ESPP (in shares)		2,235
BALANCE at Sep. 30, 2020	$ 879,636	$ 490	628,051	307,144	(14,767)	$ (41,284)	$ 2
BALANCE (in shares) at Sep. 30, 2020	49,008,915	49,008,915				1,365,648	200,000
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 Loss	138,337			138,337
Other comprehensive income (loss)	3,263				3,263
Cash dividend	(28,447)			(28,447)
Issuance of common stock to employees	22,543	$ 1	22,542
Issuance of common stock to employees (in shares)		62,501
Shares withheld for employee taxes	(14,880)		(14,880)
Shares withheld for employee taxes (in shares)		28,733
Issuance of common stock to Board of Directors and Scientific Advisory Board	1,352		1,352
Issuance of common stock to Board of Directors and Scientific Advisory Board (in shares)		7,157
Issuance of common stock to employees under an ESPP	1,440		1,440
Issuance of common stock to employees under an ESPP (in shares)		6,508
BALANCE at Sep. 30, 2021	1,036,322	$ 491	646,049	463,820	(32,756)	$ (41,284)	$ 2
BALANCE (in shares) at Sep. 30, 2021		49,060,909				1,365,648	200,000
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
Net Income Loss	46,109			46,109
Other comprehensive income (loss)	1,016				1,016
Cash dividend	(9,477)			(9,477)
Issuance of common stock to employees	8,131		8,131
Issuance of common stock to employees (in shares)		5,111
Shares withheld for employee taxes	(1,862)		(1,862)
Shares withheld for employee taxes (in shares)		(2,025)
Issuance of common stock to Board of Directors and Scientific Advisory Board	348		348
Issuance of common stock to Board of Directors and Scientific Advisory Board (in shares)		1,361
Issuance of common stock to employees under an ESPP	441		441
Issuance of common stock to employees under an ESPP (in shares)		2,403
BALANCE at Sep. 30, 2021	$ 1,036,322	$ 491	$ 646,049	$ 463,820	$ (32,756)	$ (41,284)	$ 2
BALANCE (in shares) at Sep. 30, 2021		49,060,909				1,365,648	200,000