CONSOLIDATED STATEMENTS OF SHAREHOLDERS (DEFICIT) EQUITY (UNAUDITED) - USD ($) shares in Thousands, $ 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
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
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
Balance at Dec. 31, 2018	$ 1,494	1,192,813	(1,183,335)	10,972
Balance (in shares) at Dec. 31, 2018	149,400
Increase (Decrease) in Shareholders' (Deficit) Equity
Net income (loss)				(87,197)
Balance at Jun. 30, 2019	$ 1,498	1,200,860	(1,270,532)	(68,174)
Balance (in shares) at Jun. 30, 2019	149,885
Balance at Mar. 31, 2019	$ 1,494	1,197,988	(1,227,086)	(27,604)
Balance (in shares) at Mar. 31, 2019	149,425
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
Restricted stock award, net of forfeitures	$ 1	(1)
Restricted stock award, net of forfeitures (in shares)	106
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
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
Restricted stock award, net of forfeitures (in shares)	(227)
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
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
Restricted stock award, net of forfeitures	$ (4)	4
Restricted stock award, net of forfeitures (in shares)	(293)
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			150,136
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
Issuance of common stock	$ 245	97,499		97,744
Issuance of common stock (in shares)	24,524
Restricted stock units vested (in shares)	2
Restricted stock award, net of forfeitures	$ (4)	4
Restricted stock award, net of forfeitures (in shares)	(487)
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
Balance at Dec. 31, 2019	$ 1,501	1,209,846	(1,287,468)	$ (76,121)
Balance (in shares) at Dec. 31, 2019	150,136			150,136
Increase (Decrease) in Shareholders' (Deficit) Equity
Net income (loss)				$ (53,386)
Balance at Jun. 30, 2020	$ 1,745	1,314,586	(1,340,854)	$ (24,523)
Balance (in shares) at Jun. 30, 2020	174,540			174,540
Balance at Mar. 31, 2020	$ 1,743	1,310,710	(1,316,556)	$ (4,103)
Balance (in shares) at Mar. 31, 2020	174,261
Increase (Decrease) in Shareholders' (Deficit) Equity
Net income (loss)			(24,298)	(24,298)
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan	$ 1	424		425
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan (in shares)	122
Restricted stock units vested	$ 1	(1)
Restricted stock units vested (in shares)	157
Stock option and restricted stock compensation expense		3,409		3,409
Directors' deferred share unit compensation		45		45
Adjustment of issuance costs		(1)		(1)
Balance at Jun. 30, 2020	$ 1,745	$ 1,314,586	$ (1,340,854)	$ (24,523)
Balance (in shares) at Jun. 30, 2020	174,540			174,540