Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	At-the-market Offering [Member] Common Stock [Member]	At-the-market Offering [Member] Common Stock Subscribed [Member]	At-the-market Offering [Member] Additional Paid-in Capital [Member]	At-the-market Offering [Member] Retained Earnings [Member]	At-the-market Offering [Member] AOCI Attributable to Parent [Member]	At-the-market Offering [Member] Subscription Receivable [Member]	At-the-market Offering [Member] Treasury Stock [Member]	At-the-market Offering [Member]	Public Offering [Member] Common Stock [Member]	Public Offering [Member] Common Stock Subscribed [Member]	Public Offering [Member] Additional Paid-in Capital [Member]	Public Offering [Member] Retained Earnings [Member]	Public Offering [Member] AOCI Attributable to Parent [Member]	Public Offering [Member] Subscription Receivable [Member]	Public Offering [Member] Treasury Stock [Member]	Public Offering [Member]	Common Stock [Member]	Common Stock Subscribed [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Subscription Receivable [Member]	Treasury Stock [Member]	Total
Balance (in shares) at Dec. 31, 2017																	71,325	320					(200)
Balance at Dec. 31, 2017																	$ 93		$ 609,829	$ (541,586)	$ (33)	$ (2,109)	$ (2,741)	$ 63,453
Net loss																				(13,424)				(13,424)
Foreign currency translation adjustments																					(18)			(18)
Stock-based compensation expense																			1,048					1,048
Issuance of common stock issued (in shares)	1,537	(320)
Issuance of common stock issued	$ 2		$ 7,414			$ 2,109		$ 9,525
Cumulative effect of ASU 2014-09 adoption																				35				35
Subscription of common stock in connection with at-the-market offering, net of commissions (in shares)																		103
Subscription of common stock in connection with at-the-market offering, net of commissions																			750			(750)
Balance (in shares) at Mar. 31, 2018																	72,862	103					(200)
Balance at Mar. 31, 2018																	$ 95		619,041	(554,975)	(51)	(750)	$ (2,741)	60,619
Balance (in shares) at Dec. 31, 2017																	71,325	320					(200)
Balance at Dec. 31, 2017																	$ 93		609,829	(541,586)	(33)	(2,109)	$ (2,741)	63,453
Net loss																								(52,953)
Foreign currency translation adjustments																								(60)
Balance (in shares) at Sep. 30, 2018																	84,742						(200)
Balance at Sep. 30, 2018																	$ 110		712,111	(594,504)	(93)		$ (2,741)	114,883
Balance (in shares) at Mar. 31, 2018																	72,862	103					(200)
Balance at Mar. 31, 2018																	$ 95		619,041	(554,975)	(51)	(750)	$ (2,741)	60,619
Net loss																				(15,172)				(15,172)
Foreign currency translation adjustments																					(38)			(38)
Stock-based compensation expense																			2,130					2,130
Issuance of common stock issued (in shares)	2,097
Issuance of common stock issued	$ 2		15,288					15,290
Subscription of common stock in connection with at-the-market offering, net of commissions (in shares)																		(103)
Subscription of common stock in connection with at-the-market offering, net of commissions																			(750)			750
Balance (in shares) at Jun. 30, 2018																	74,959						(200)
Balance at Jun. 30, 2018																	$ 97		635,709	(570,147)	(89)		$ (2,741)	62,829
Net loss																				(24,357)				(24,357)
Foreign currency translation adjustments																					(4)			(4)
Stock-based compensation expense																			1,123					1,123
Issuance of common stock issued (in shares)	596								9,091
Issuance of common stock issued	$ 1		$ 4,837					$ 4,838	$ 12		$ 69,975					$ 69,987
Exercise of stock options (in shares)																	96
Exercise of stock options																			467					467
Balance (in shares) at Sep. 30, 2018																	84,742						(200)
Balance at Sep. 30, 2018																	$ 110		712,111	(594,504)	(93)		$ (2,741)	114,883
Balance (in shares) at Dec. 31, 2018																	84,742						(200)
Balance at Dec. 31, 2018																	$ 110		713,019	(609,208)	(105)		$ (2,741)	101,075
Net loss																				(18,735)				(18,735)
Foreign currency translation adjustments																					(42)			(42)
Stock-based compensation expense																			1,077					1,077
Balance (in shares) at Mar. 31, 2019																	84,742						(200)
Balance at Mar. 31, 2019																	$ 110		714,096	(627,943)	(147)		$ (2,741)	83,375
Balance (in shares) at Dec. 31, 2018																	84,742						(200)
Balance at Dec. 31, 2018																	$ 110		713,019	(609,208)	(105)		$ (2,741)	101,075
Net loss																								(57,277)
Foreign currency translation adjustments																								$ (200)
Exercise of stock options (in shares)																								247
Balance (in shares) at Sep. 30, 2019																	86,621						(200)
Balance at Sep. 30, 2019																	$ 112		725,356	(666,485)	(305)		$ (2,741)	$ 55,937
Balance (in shares) at Mar. 31, 2019																	84,742						(200)
Balance at Mar. 31, 2019																	$ 110		714,096	(627,943)	(147)		$ (2,741)	83,375
Net loss																				(19,700)				(19,700)
Foreign currency translation adjustments																					53			53
Stock-based compensation expense																			994					994
Issuance of common stock issued (in shares)																	1,632
Issuance of common stock issued																	$ 2		7,737					7,739
Exercise of stock options (in shares)																	50
Exercise of stock options																			267					267
Subscription receivable in connection with exercise of stock options (in shares)																		175
Subscription receivable in connection with exercise of stock options																			933			(933)
Balance (in shares) at Jun. 30, 2019																	86,424	175					(200)
Balance at Jun. 30, 2019																	$ 112		724,027	(647,643)	(94)	(933)	$ (2,741)	72,728
Net loss																				(18,842)				(18,842)
Foreign currency translation adjustments																					(211)			(211)
Stock-based compensation expense																			1,216					1,216
Exercise of stock options (in shares)																	22
Exercise of stock options																			113					113
Subscription receivable in connection with exercise of stock options (in shares)																	175	(175)
Subscription receivable in connection with exercise of stock options																						933		933
Balance (in shares) at Sep. 30, 2019																	86,621						(200)
Balance at Sep. 30, 2019																	$ 112		$ 725,356	$ (666,485)	$ (305)		$ (2,741)	$ 55,937