CONSOLIDATED STATEMENT OF SHAREHOLDERS' EQUITY (UNAUDITED) - USD ($)	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, 2017	$ 659,054,000	$ 485,000	$ 611,063,000	$ 99,126,000	$ (11,464,000)	$ (40,158,000)	$ 2,000
BALANCE (in shares) at Dec. 31, 2017		48,476,034				1,357,863	200,000
ASC Topic 606 Adoption at Dec. 31, 2017	(17,894,000)			(17,894,000)
ADJUSTED BALANCE at Dec. 31, 2017	641,160,000	$ 485,000	611,063,000	81,232,000	(11,464,000)	$ (40,158,000)	$ 2,000
BALANCE ADJUSTED (in shares) at Dec. 31, 2017		48,476,034				1,357,863	200,000
Net income	5,959,000			5,959,000
Other comprehensive income	496,000				496,000
Cash dividend	(2,831,000)			(2,831,000)
Issuance of common stock to employees	2,724,000	$ 1,000	2,723,000
Issuance of common stock to employees (in shares)		130,911
Shares withheld for employee taxes	(5,832,000)		(5,832,000)
Shares withheld for employee taxes (in shares)		(48,707)
Common shares repurchased	$ (477,000)					$ (477,000)
Common shares repurchased (in shares)	3,774					3,774
Issuance of common stock to Board of Directors and Scientific Advisory Board	$ 1,197,000		1,197,000
Issuance of common stock to Board of Directors and Scientific Advisory Board (in shares)		13,482
Issuance of common stock to employees under an ESPP	253,000		253,000
Issuance of common stock to employees under an ESPP (in shares)		2,345
BALANCE at Mar. 31, 2018	642,649,000	$ 486,000	609,404,000	84,360,000	(10,968,000)	$ (40,635,000)	$ 2,000
BALANCE (in shares) at Mar. 31, 2018		48,574,065				1,361,637	200,000
BALANCE at Dec. 31, 2018	690,506,000	$ 487,000	617,334,000	129,552,000	(16,234,000)	$ (40,635,000)	$ 2,000
BALANCE (in shares) at Dec. 31, 2018		48,681,524				1,361,637	200,000
Net income	31,474,000			31,474,000
Other comprehensive income	714,000				714,000
Cash dividend	(4,717,000)			(4,717,000)
Issuance of common stock to employees	3,537,000	$ 1,000	3,536,000
Issuance of common stock to employees (in shares)		107,213
Shares withheld for employee taxes	(5,757,000)		(5,757,000)
Shares withheld for employee taxes (in shares)		(38,755)
Common shares repurchased	$ (649,000)					$ (649,000)
Common shares repurchased (in shares)	4,011					4,011
Issuance of common stock to Board of Directors and Scientific Advisory Board	$ 816,000		816,000
Issuance of common stock to Board of Directors and Scientific Advisory Board (in shares)		7,758
Issuance of common stock to employees under an ESPP	277,000		277,000
Issuance of common stock to employees under an ESPP (in shares)		2,571
BALANCE at Mar. 31, 2019	$ 716,201,000	$ 488,000	$ 616,206,000	$ 156,309,000	$ (15,520,000)	$ (41,284,000)	$ 2,000
BALANCE (in shares) at Mar. 31, 2019		48,760,311				1,365,648,000	200,000