CONSOLIDATED STATEMENT OF SHAREHOLDERS' EQUITY - 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, 2016					$ (10,666,000)
Net income	$ 57,552,000
Other comprehensive income	(905,000)
BALANCE at Jun. 30, 2017					(11,571,000)
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	16,773,000			16,773,000
Other comprehensive income	1,013,000				1,013,000
Cash dividend	(5,659,000)			(5,659,000)
Issuance of common stock to employees	6,035,000	$ 3,000	6,032,000
Issuance of common stock to employees (in shares)		250,979
Shares withheld for employee taxes	(11,031,000)	$ (1,000)	(11,030,000)
Shares withheld for employee taxes (in shares)		(101,581)
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	$ 2,303,000		2,303,000
Issuance of common stock to Board of Directors and Scientific Advisory Board (in shares)		19,732
Issuance of common stock to employees under an ESPP	564,000		564,000
Issuance of common stock to employees under an ESPP (in shares)		5,532
BALANCE at Jun. 30, 2018	$ 650,681,000	$ 487,000	$ 608,932,000	$ 92,346,000	$ (10,451,000)	$ (40,635,000)	$ 2,000
BALANCE (in shares) at Jun. 30, 2018		48,650,696				1,361,637,000	200,000