Consolidated Statements of Stockholders' Equity - 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] Receivables from Stockholder [Member]	At-the-market Offering [Member] Treasury Stock [Member]	At-the-market Offering [Member] Noncontrolling Interest [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] Receivables from Stockholder [Member]	Public Offering [Member] Treasury Stock [Member]	Public Offering [Member] Noncontrolling Interest [Member]	Public Offering [Member]	Common Stock [Member]	Common Stock Subscribed [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Receivables from Stockholder [Member]	Treasury Stock [Member]	Noncontrolling Interest [Member]	Total
Balance (in shares) at Dec. 31, 2015																			70,146						(200)
Balance at Dec. 31, 2015																			$ 91		$ 594,511	$ (501,379)	$ (26)		$ (2,741)	$ 205	$ 90,661
Net (loss) income																						10,806				(73)	10,733
Purchase of noncontrolling interests																					(239)					(129)	(368)
Foreign currency translation adjustment																							(59)			(3)	(62)
Stock-based compensation expense																					2,457						2,457
Exercise of stock options (in shares)																			244
Exercise of stock options																			$ 1		1,340						1,341
Balance (in shares) at Dec. 31, 2016																			70,390						(200)
Balance at Dec. 31, 2016																			$ 92		598,069	(490,573)	(85)		$ (2,741)		104,762
Net (loss) income																						(51,013)					(51,013)
Foreign currency translation adjustment																							52				52
Stock-based compensation expense																					4,142						4,142
Exercise of stock options (in shares)																			80
Exercise of stock options																					469						469
Return of purchase premium for noncontrolling interests																					15						15
Issuance of common stock in connection with at-the-market offering, net of commissions and issuance costs (in shares)	855
Issuance of common stock	$ 1		$ 5,025						$ 5,026
Subscription of common stock in connection with at-the-market offering, net of commissions (in shares)																				320
Subscription of common stock in connection with at-the-market offering, net of commissions																					2,109			$ (2,109)
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) income																						(67,657)					(67,657)
Foreign currency translation adjustment																							(72)				(72)
Stock-based compensation expense																					5,209						$ 5,209
Exercise of stock options (in shares)																			96								96
Exercise of stock options																					467						$ 467
Issuance of common stock in connection with at-the-market offering, net of commissions and issuance costs (in shares)	4,230	(320)							3,900	9,091								9,100
Issuance of common stock	$ 5		$ 27,539			$ 2,109			$ 29,653	$ 12		$ 69,975						$ 69,987
Cumulative effect of ASU 2014-09 adoption																						35					35
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