CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Total
Balance at Dec. 31, 2019	$ 1,501	$ 1,209,846	$ (1,287,468)	$ (76,121)
Balance (in shares) at Dec. 31, 2019	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 award forfeitures	$ (5)	5
Restricted stock award forfeitures (in shares)	(487)
Restricted stock units vested	$ 4	(4)
Restricted stock units vested (in shares)	395
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
Increase (Decrease) in Shareholders' Equity (Deficit)
Net loss			(139,303)	(139,303)
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan	$ 10	3,759		3,769
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan (in shares)	998
Issuance of common stock, net of issuance costs	$ 242	153,788		154,030
Issuance of common stock, net of issuance costs (in shares)	24,181
Conversion of convertible senior notes	$ 3	997		1,000
Conversion of convertible senior notes (in shares)	239
Issuance of pre-funded warrants, net of issuance costs		199,045		199,045
Restricted stock award forfeitures	$ (1)	1
Restricted stock award forfeitures (in shares)	(57)
Restricted stock units vested (in shares)	2
Stock option and restricted stock compensation expense		16,794		16,794
Directors' deferred share unit compensation		681		681
Balance at Dec. 31, 2021	$ 2,204	1,794,525	(1,471,143)	$ 325,586
Balance (in shares) at Dec. 31, 2021	220,361			220,361
Increase (Decrease) in Shareholders' Equity (Deficit)
Net loss			(222,929)	$ (222,929)
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan	$ 5	1,900		1,905
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan (in shares)	491
Issuance of common stock, net of issuance costs	$ 51	25,598		25,649
Issuance of common stock, net of issuance costs (in shares)	5,167
Restricted stock units vested (in shares)	27
Stock option and restricted stock compensation expense		24,899		24,899
Directors' deferred share unit compensation		716		716
Balance at Dec. 31, 2022	$ 2,260	$ 1,847,638	$ (1,694,072)	$ 155,826
Balance (in shares) at Dec. 31, 2022	226,046			226,046