CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]	Series A Nonconvertible Preferred Stock [Member] Preferred Stock [Member]
BALANCE (in shares) at Dec. 31, 2012		46,561,437				205,902,000	200,000
BALANCE at Dec. 31, 2012	$ 350,235	$ 465	$ 564,883	$ (204,211)	$ (5,702)	$ (5,202)	$ 2
Increase (Decrease) in Shareholders' Equity [Roll Forward]
Net income	74,052			74,052
Other comprehensive income	1,334				1,334
Repurchase of common stock (in shares)						195,599,000
Repurchase of common stock	(5,456)					$ (5,456)
Exercise of common stock options and warrants, net of tendered shares (in shares)		223,714
Exercise of common stock options, net of tendered shares	2,558	$ 2	2,556
Issuance of common stock to employees, net of shares withheld for employee taxes (in shares)		(13,502)
Issuance of common stock to employees, net of shares withheld for employee taxes	3,519	$ 0	3,519
Issuance of common stock to Board of Directors and Scientific Advisory Board (in shares)		39,153
Issuance of common stock to Board of Directors and Scientific Advisory Board	1,101	$ 1	1,100
Issuance of common stock to employees under an Employee Stock Purchase Plan (ESPP) (in shares)		14,366
Issuance of common stock to employees under an ESPP	343	$ 0	343
BALANCE (in shares) at Dec. 31, 2013		46,825,168				401,501,000	200,000
BALANCE at Dec. 31, 2013	427,686	$ 468	572,401	(130,159)	(4,368)	$ (10,658)	$ 2
Increase (Decrease) in Shareholders' Equity [Roll Forward]
Net income	41,854			41,854
Other comprehensive income	(14)				(14)
Repurchase of common stock (in shares)						956,362,000
Repurchase of common stock	(29,500)					$ (29,500)
Exercise of common stock options and warrants, net of tendered shares (in shares)		184,798
Exercise of common stock options, net of tendered shares	1,887	$ 3	1,884
Issuance of common stock to employees (shares)		83,834
Issuance of common stock to employees	8,027	$ 1	8,026
Shares withheld for employee taxes (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	$ 0	1,318
Issuance of common stock to employees under an Employee Stock Purchase Plan (ESPP) (in shares)		12,373
Issuance of common stock to employees under an ESPP	328	$ 0	328
BALANCE (in shares) at Dec. 31, 2014		47,061,826				1,357,863,000	200,000
BALANCE at Dec. 31, 2014	448,742	$ 471	581,114	(88,305)	(4,382)	$ (40,158)	$ 2
Increase (Decrease) in Shareholders' Equity [Roll Forward]
Net income	14,678
Other comprehensive income	(5,437)				(5,437)
Exercise of common stock options and warrants, net of tendered shares (in shares)		340,725
Exercise of common stock options, net of tendered shares	2,034	$ 3	2,031
Issuance of common stock to employees (shares)		798,036
Issuance of common stock to employees	10,047	$ 8	10,039
Shares withheld for employee taxes (shares)		(124,961)
Shares withheld for employee taxes	(5,337)	$ 0	(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	$ 0	1,591
Issuance of common stock to employees under an Employee Stock Purchase Plan (ESPP) (in shares)		12,246
Issuance of common stock to employees under an ESPP	447	$ 0	447
BALANCE (in shares) at Dec. 31, 2015		48,132,223				1,357,863,000	200,000
BALANCE at Dec. 31, 2015	$ 466,765	$ 482	$ 589,885	$ (73,627)	$ (9,819)	$ (40,158)	$ 2