CONSOLIDATED STATEMENTS OF SHAREHOLDERS' (DEFICIT) EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Total
Increase (Decrease) in Shareholders' (Deficit) Equity
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	132,526,000
Increase (Decrease) in Shareholders' (Deficit) Equity
Net loss			(38,613)	(38,613)
Issuance of common stock pursuant to the exercise of stock options	$ 4	2,255		2,259
Issuance of common stock pursuant to the exercise of stock options (in shares)	421,000
Stock option and restricted stock compensation expense		3,746		3,746
Directors' deferred share units converted	$ 1	(1)
Directors' deferred share units converted (in shares)	77,000
Directors' deferred share unit compensation		102		102
Balance at Mar. 31, 2018	$ 1,330	1,015,464	(1,053,105)	(36,311)
Balance (in shares) at Mar. 31, 2018	133,024,000
Balance at Dec. 31, 2017	$ 1,325	1,009,362	(1,028,582)	(17,895)
Balance (in shares) at Dec. 31, 2017	132,526,000
Increase (Decrease) in Shareholders' (Deficit) Equity
Net loss				(127,044)
Balance at Sep. 30, 2018	$ 1,490	1,186,935	(1,141,536)	46,889
Balance (in shares) at Sep. 30, 2018	149,049,000
Balance at Mar. 31, 2018	$ 1,330	1,015,464	(1,053,105)	(36,311)
Balance (in shares) at Mar. 31, 2018	133,024,000
Increase (Decrease) in Shareholders' (Deficit) Equity
Net loss			(41,624)	(41,624)
Issuance of common stock pursuant to the exercise of stock options	$ 1	558		559
Issuance of common stock pursuant to the exercise of stock options (in shares)	146,000
Issuance of common stock	$ 158	162,382		162,540
Issuance of common stock (in shares)	15,755,000
Stock option and restricted stock compensation expense		3,971		3,971
Directors' deferred share units converted	$ 1			1
Directors' deferred share units converted (in shares)	96,000
Directors' deferred share unit compensation		54		54
Balance at Jun. 30, 2018	$ 1,490	1,182,429	(1,094,729)	89,190
Balance (in shares) at Jun. 30, 2018	149,021,000
Increase (Decrease) in Shareholders' (Deficit) Equity
Net loss			(46,807)	(46,807)
Issuance of common stock pursuant to the exercise of stock options		124		124
Issuance of common stock pursuant to the exercise of stock options (in shares)	28,000
Issuance of common stock		(28)		(28)
Stock option and restricted stock compensation expense		4,308		4,308
Directors' deferred share unit compensation		102		102
Balance at Sep. 30, 2018	$ 1,490	1,186,935	(1,141,536)	46,889
Balance (in shares) at Sep. 30, 2018	149,049,000
Increase (Decrease) in Shareholders' (Deficit) Equity
Net loss			(41,799)	(41,799)
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan	$ 4	1,355		1,359
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan (in shares)	351,000
Stock option and restricted stock compensation expense		4,420		4,420
Directors' deferred share unit compensation		103		103
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			149,400,000
Increase (Decrease) in Shareholders' (Deficit) Equity
Net 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			149,400,000
Increase (Decrease) in Shareholders' (Deficit) Equity
Net loss				$ (108,947)
Issuance of common stock pursuant to the exercise of stock options (in shares)				86,000
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			149,688,000
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 loss			(43,446)	(43,446)
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan	$ 3	667		670
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan (in shares)	354,000
Restricted stock award	$ 1	(1)
Restricted stock award (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 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 (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			149,688,000