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	38,155			38,155
Other comprehensive income	2,460				2,460
Cash dividend	(7,098)			(7,098)
Issuance of common stock to employees	5,665		5,665
Issuance of common stock to employees (in shares)		80,483
Shares withheld for employee taxes	$ (4,816)		(4,816)
Shares withheld for employee taxes (in shares)		(30,437)
Common shares repurchased (in shares)	0
Issuance of common stock to Board of Directors and Scientific Advisory Board	$ 554		554
Issuance of common stock to Board of Directors and Scientific Advisory Board (in shares)		5,678
Issuance of common stock to employees under an ESPP	328		328
Issuance of common stock to employees under an ESPP (in shares)		2,315
BALANCE at Mar. 31, 2020	846,697	$ 489	621,967	280,060	(14,537)	$ (41,284)	$ 2
BALANCE (in shares) at Mar. 31, 2020		48,910,232				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	51,687			51,687
Other comprehensive income	1,010				1,010
Cash dividend	(9,487)			(9,487)
Issuance of common stock to employees	5,116	$ 1	5,115
Issuance of common stock to employees (in shares)		53,123
Shares withheld for employee taxes	$ (9,634)		(9,634)
Shares withheld for employee taxes (in shares)		(22,048)
Common shares repurchased (in shares)	0
Issuance of common stock to Board of Directors and Scientific Advisory Board	$ 630		630
Issuance of common stock to Board of Directors and Scientific Advisory Board (in shares)		4,443
Issuance of common stock to employees under an ESPP	432		432
Issuance of common stock to employees under an ESPP (in shares)		1,782
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