CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Loss [Member]	Treasury Stock [Member]	Series A Nonconvertible Preferred Stock [Member] Preferred Stock [Member]
BALANCE (in shares) at Dec. 31, 2013		46,825,168				401,501	200,000
BALANCE at Dec. 31, 2013	$ 427,686	$ 468	$ 572,401	$ (130,159)	$ (4,368)	$ (10,658)	$ 2
Net income	41,854			41,854
Other comprehensive loss	(14)				(14)
Repurchase of Common stock (in shares)						956,362
Repurchase of Common Stock	(29,500)					$ (29,500)
Exercise of common stock options (in shares)		184,798
Exercise of common stock options	1,887	$ 3	1,884
Issuance of common stock to employees (in shares)		83,834
Issuance of common stock to employees	8,027	$ 1	8,026
Shares withheld for employee taxes (in shares)		(83,831)
Shares withheld for employee taxes	(2,844)	$ (1)	(2,843)
Issuance of common stock to Board of Directors and Scientific Advisory Board (in shares)		39,484
Issuance of common stock to Board of Directors and Scientific Advisory Board	1,318		1,318
Issuance of common stock to employees under an ESPP (in shares)		12,373
Issuance of common stock to employees under an ESPP	328		328
BALANCE (in shares) at Dec. 31, 2014		47,061,826				1,357,863	200,000
BALANCE at Dec. 31, 2014	448,742	$ 471	581,114	(88,305)	(4,382)	$ (40,158)	$ 2
Net income	14,678			14,678
Other comprehensive loss	(5,437)				(5,437)
Exercise of common stock options (in shares)		340,725
Exercise of common stock options	2,034	$ 3	2,031
Issuance of common stock to employees (in shares)		798,036
Issuance of common stock to employees	10,047	$ 8	10,039
Shares withheld for employee taxes (in shares)		(124,961)
Shares withheld for employee taxes	(5,337)		(5,337)
Issuance of common stock to Board of Directors and Scientific Advisory Board (in shares)		44,351
Issuance of common stock to Board of Directors and Scientific Advisory Board	1,591		1,591
Issuance of common stock to employees under an ESPP (in shares)		12,246
Issuance of common stock to employees under an ESPP	447		447
BALANCE (in shares) at Dec. 31, 2015		48,132,223				1,357,863	200,000
BALANCE at Dec. 31, 2015	466,765	$ 482	589,885	(73,627)	(9,819)	$ (40,158)	$ 2
Net income	48,070			48,070
Other comprehensive loss	$ (847)				(847)
Exercise of common stock options (in shares)	12,750	12,750
Exercise of common stock options	$ 185		185
Issuance of common stock to employees (in shares)		165,826
Issuance of common stock to employees	12,356	$ 2	12,354
Shares withheld for employee taxes (in shares)		(92,241)
Shares withheld for employee taxes	(4,871)	$ (1)	(4,870)
Excess tax benefits from share-based payment arrangements	4,232		4,232
Issuance of common stock to Board of Directors and Scientific Advisory Board (in shares)		43,046
Issuance of common stock to Board of Directors and Scientific Advisory Board	2,012		2,012
Issuance of common stock to employees under an ESPP (in shares)		9,386
Issuance of common stock to employees under an ESPP	566		566
BALANCE (in shares) at Dec. 31, 2016		48,270,990				1,357,863	200,000
BALANCE at Dec. 31, 2016	$ 528,468	$ 483	$ 604,364	$ (25,557)	$ (10,666)	$ (40,158)	$ 2