Condensed Consolidated Statements of Stockholders' (Deficit) Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-in-Capital	Accumulated Other Comprehensive Income	Treasury Stock	Accumulated Deficit	Total
Balance at Dec. 31, 2017	$ 2,291	$ 1,250,899	$ 2,194	$ (3,102)	$ (1,178,636)	$ 73,646
Balance (in shares) at Dec. 31, 2017	229,073,517			587,151
Increase (Decrease) in Stockholders' Equity
Net loss attributable to the Company					(61,268)	(61,268)
Other comprehensive income/loss			(432)			(432)
Stock-based compensation	$ 5	6,384				6,389
Stock-based compensation (in shares)	450,270
Stock dividend		39			(39)
Stock dividend (in shares)	20,245
Issuance of common stock, net	$ 26	4,886				4,912
Issuance of common stock, net (in shares)	2,560,849
Stock option exercises	$ 4	123		$ (35)		92
Stock option exercises (in shares)	406,412			17,606
Equity component of convertible senior notes, net of issuance costs and income tax benefit		30,121				30,121
Purchase of capped call		(16,000)				(16,000)
Purchase of common stock forward				$ (27,500)		(27,500)
Purchase of common stock forward (in shares)				14,397,906
Exercise of warrants (in shares)	100
Provision for common stock warrants		7,932				7,932
Balance at Sep. 30, 2018	$ 2,326	1,284,384	1,762	$ (30,637)	(1,243,430)	14,405
Balance (in shares) at Sep. 30, 2018	232,511,393			15,002,663
Balance at Jun. 30, 2018	$ 2,297	1,276,989	1,844	$ (30,637)	(1,224,365)	26,128
Balance (in shares) at Jun. 30, 2018	229,655,825			15,002,663
Increase (Decrease) in Stockholders' Equity
Net loss attributable to the Company					(15,565)	(15,565)
Other comprehensive income/loss			(82)			(82)
Stock-based compensation	$ 3	2,061				2,064
Stock-based compensation (in shares)	247,747
Stock dividend		13			(13)
Stock dividend (in shares)	6,972
Issuance of common stock, net	$ 26	4,876				4,902
Issuance of common stock, net (in shares)	2,560,849
Stock option exercises		26				26
Stock option exercises (in shares)	40,000
Equity component of convertible senior notes, net of issuance costs and income tax benefit		(1,707)				(1,707)
Provision for common stock warrants		2,126				2,126
Balance at Sep. 30, 2018	$ 2,326	1,284,384	1,762	$ (30,637)	(1,243,430)	14,405
Balance (in shares) at Sep. 30, 2018	232,511,393			15,002,663
Increase (Decrease) in Stockholders' Equity
Cumulative effect from adoption of ASC 842					(3,487)	(3,487)
Balance at Dec. 31, 2018	$ 2,342	1,289,714	1,584	$ (30,637)	(1,260,290)	$ 2,713
Balance (in shares) at Dec. 31, 2018	234,160,661			15,002,663		234,160,661
Increase (Decrease) in Stockholders' Equity
Net loss attributable to the Company					(73,728)	$ (73,728)
Other comprehensive income/loss			(655)			(655)
Stock-based compensation	$ 17	7,910				7,927
Stock-based compensation (in shares)	1,715,454
Stock dividend		39			(39)
Stock dividend (in shares)	15,067
Issuance of common stock, net	$ 163	37,935				38,098
Issuance of common stock, net (in shares)	16,333,585
Stock option exercises	$ 3	460		$ (579)		(116)
Stock option exercises (in shares)	258,409			256,382
Provision for common stock warrants		10,244				10,244
Accretion of discount, preferred stock		(772)				(772)
Conversion of preferred stock	$ 15	1,868				1,883
Conversion of preferred stock (in shares)	1,499,402
Balance at Sep. 30, 2019	$ 2,540	1,347,398	929	$ (31,216)	(1,334,057)	$ (14,406)
Balance (in shares) at Sep. 30, 2019	253,982,578			15,259,045		253,982,578
Balance at Jun. 30, 2019	$ 2,470	1,328,911	1,460	$ (30,681)	(1,312,815)	$ (10,655)
Balance (in shares) at Jun. 30, 2019	246,975,173			15,020,437
Increase (Decrease) in Stockholders' Equity
Net loss attributable to the Company					(21,229)	(21,229)
Other comprehensive income/loss			(531)			(531)
Stock-based compensation	$ 9	2,795				2,804
Stock-based compensation (in shares)	934,469
Stock dividend		13			(13)
Stock dividend (in shares)	4,920
Issuance of common stock, net	$ 45	9,790				9,835
Issuance of common stock, net (in shares)	4,451,948
Stock option exercises	$ 1	211		$ (535)		(323)
Stock option exercises (in shares)	116,666			238,608
Provision for common stock warrants		4,582				4,582
Accretion of discount, preferred stock		(772)				(772)
Conversion of preferred stock	$ 15	1,868				1,883
Conversion of preferred stock (in shares)	1,499,402
Balance at Sep. 30, 2019	$ 2,540	$ 1,347,398	$ 929	$ (31,216)	$ (1,334,057)	$ (14,406)
Balance (in shares) at Sep. 30, 2019	253,982,578			15,259,045		253,982,578