CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (DEFICIT) - USD ($) shares in Thousands, $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Deficit Adjustment	Accumulated Deficit	Adjustment	Total
Increase (Decrease) in Shareholders' Equity (Deficit)
Transition adjustment for ASC 606			$ 14,090		$ 14,090
Balance at Dec. 31, 2017	$ 1,325	$ 1,009,362		$ (1,028,582)		$ (17,895)
Balance (in shares) at Dec. 31, 2017	132,526
Increase (Decrease) in Shareholders' Equity (Deficit)
Net loss				(168,843)		(168,843)
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan	$ 9	4,292				4,301
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan (in shares)	946
Issuance of common stock, net of issuance costs	$ 158	162,354				162,512
Issuance of common stock, net of issuance costs (in shares)	15,755
Stock option and restricted stock compensation expense		16,445				16,445
Directors' deferred share units converted	$ 2	(1)				1
Directors' deferred share units converted (in shares)	173
Directors' deferred share unit compensation		361				361
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' Equity (Deficit)
Net loss				(104,133)		(104,133)
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan	$ 11	2,862				2,873
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan (in shares)	1,150
Stock options exercised		13,830				13,830
Restricted stock award, net of forfeitures	$ (4)	4
Restricted stock award, net of forfeitures (in shares)	(414)
Directors' deferred share unit compensation		337				337
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' Equity (Deficit)
Net loss				(44,372)		$ (44,372)
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan	$ 5	1,466				1,471
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan (in shares)	458
Issuance of common stock, net of issuance costs	$ 445	193,826				194,271
Issuance of common stock, net of issuance costs (in shares)	44,496
Restricted stock units vested	$ 4	(4)
Restricted stock units vested (in shares)	395
Restricted stock award forfeitures	$ (5)	5
Restricted stock award forfeitures (in shares)	(487)
Stock option and restricted stock compensation expense		13,978				13,978
Directors' deferred share unit compensation		343				343
Balance at Dec. 31, 2020	$ 1,950	$ 1,419,460		$ (1,331,840)		$ 89,570
Balance (in shares) at Dec. 31, 2020	194,998					194,998