CONSOLIDATED STATEMENTS OF SHAREHOLDERS' (DEFICIT) EQUITY (UNAUDITED) - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Total
Balance at Dec. 31, 2018	$ 1,494	$ 1,192,813	$ (1,183,335)	$ 10,972
Balance (in shares) at Dec. 31, 2018	149,400,000
Increase (Decrease) in Shareholders' (Deficit) Equity
Net income (loss)			(43,751)	(43,751)
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan		68		68
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan (in shares)	25,000
Stock option and restricted stock compensation expense		5,007		5,007
Directors' deferred share unit compensation		100		100
Balance at Mar. 31, 2019	$ 1,494	1,197,988	(1,227,086)	(27,604)
Balance (in shares) at Mar. 31, 2019	149,425,000
Balance at Dec. 31, 2018	$ 1,494	1,192,813	(1,183,335)	10,972
Balance (in shares) at Dec. 31, 2018	149,400,000
Increase (Decrease) in Shareholders' (Deficit) Equity
Net income (loss)			4,814	4,814
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan	$ 7	2,054		2,061
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan (in shares)	741,000
Restricted stock award - net of forfeitures	$ (4)	4
Restricted stock award - net of forfeitures (in shares)	(293,000)
Stock option and restricted stock compensation expense		3,138		3,138
Directors' deferred share unit compensation		91		91
Balance at Dec. 31, 2019	$ 1,501	1,209,846	(1,287,468)	$ (76,121)
Balance (in shares) at Dec. 31, 2019	150,136,000			150,136,000
Balance at Mar. 31, 2019	$ 1,494	1,197,988	(1,227,086)	$ (27,604)
Balance (in shares) at Mar. 31, 2019	149,425,000
Increase (Decrease) in Shareholders' (Deficit) Equity
Net income (loss)			(43,446)	(43,446)
Issuance of common stock	$ 3	667		670
Issuance of common stock (in shares)	354,000
Restricted stock award - net of forfeitures	$ 1	(1)
Restricted stock award - net of forfeitures (in shares)	106,000
Stock option and restricted stock compensation expense		2,106		2,106
Directors' deferred share unit compensation		100		100
Balance at Jun. 30, 2019	$ 1,498	1,200,860	(1,270,532)	(68,174)
Balance (in shares) at Jun. 30, 2019	149,885,000
Increase (Decrease) in Shareholders' (Deficit) Equity
Net income (loss)			(21,750)	(21,750)
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan		73		73
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan (in shares)	30,000
Restricted stock award - net of forfeitures (in shares)	(227,000)
Stock option and restricted stock compensation expense		3,580		3,580
Directors' deferred share unit compensation		46		46
Balance at Sep. 30, 2019	$ 1,498	1,204,559	(1,292,282)	(86,225)
Balance (in shares) at Sep. 30, 2019	149,688,000
Balance at Dec. 31, 2019	$ 1,501	1,209,846	(1,287,468)	$ (76,121)
Balance (in shares) at Dec. 31, 2019	150,136,000			150,136,000
Increase (Decrease) in Shareholders' (Deficit) Equity
Net income (loss)			(29,088)	$ (29,088)
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan	$ 1	239		$ 240
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan (in shares)	86,000
Stock options exercised (in shares)				86,000
Issuance of common stock	$ 245	97,499		$ 97,744
Issuance of common stock (in shares)	24,524,000
Restricted stock units vested (in shares)	2,000
Restricted stock award - net of forfeitures	$ (4)	4
Restricted stock award - net of forfeitures (in shares)	(487,000)
Stock option and restricted stock compensation expense		3,122		3,122
Balance at Mar. 31, 2020	$ 1,743	$ 1,310,710	$ (1,316,556)	$ (4,103)
Balance (in shares) at Mar. 31, 2020	174,261,000			174,261,000