CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Capital Contributed in Excess of Par	Treasury Stock	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interest
Beginning balance (in shares) at Dec. 31, 2018		190,446
Beginning Balance at Dec. 31, 2018	$ 265,849	$ 1,905	$ 1,219,237	$ (824)	$ (953,216)	$ (351)	$ (902)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)		1,140
Exercise of stock options, net	2,106	$ 11	3,366	(1,271)
Stock-based compensation (in shares)		15
Stock-based compensation	4,147	$ 0	4,147
Net proceeds from equity offering (in shares)		371
Issuance of common stock in public offering, net	5,829	$ 4	5,825
Other comprehensive income (loss)	(14)					(14)
Net loss	(163,357)				(163,290)		(67)
Ending balance (in shares) at Jun. 30, 2019		191,972
Ending Balance at Jun. 30, 2019	114,560	$ 1,920	1,232,575	(2,095)	(1,116,506)	(365)	(969)
Beginning balance (in shares) at Mar. 31, 2019		191,509
Beginning Balance at Mar. 31, 2019	181,804	$ 1,915	1,224,066	(2,095)	(1,040,553)	(560)	(969)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)		77
Exercise of stock options, net	281	$ 1	280
Stock-based compensation (in shares)		15
Stock-based compensation	2,404		2,404
Net proceeds from equity offering (in shares)		371
Issuance of common stock in public offering, net	5,829	$ 4	5,825
Other comprehensive income (loss)	195					195
Net loss	(75,953)				(75,953)
Ending balance (in shares) at Jun. 30, 2019		191,972
Ending Balance at Jun. 30, 2019	114,560	$ 1,920	1,232,575	(2,095)	(1,116,506)	(365)	(969)
Beginning balance (in shares) at Dec. 31, 2019		212,529
Beginning Balance at Dec. 31, 2019	267,230	$ 2,125	1,579,205	(2,095)	(1,310,406)	(568)	(1,031)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)		146
Exercise of stock options, net	1,995	$ 1	1,994
Stock-based compensation (in shares)		58
Stock-based compensation	11,098	$ 1	11,097
Issuance of common stock due to debt conversion (in shares)		1,393
Issuance of common stock due to debt conversion	7,114	$ 14	7,100
Net proceeds from equity offering (in shares)		16,947
Issuance of common stock in public offering, net	464,593	$ 170	464,423
Other comprehensive income (loss)	(227)					(227)	0
Net loss	(159,576)				(159,513)		(63)
Ending balance (in shares) at Jun. 30, 2020		231,073
Ending Balance at Jun. 30, 2020	592,227	$ 2,311	2,063,819	(2,095)	(1,469,919)	(795)	(1,094)
Beginning balance (in shares) at Mar. 31, 2020		213,929
Beginning Balance at Mar. 31, 2020	184,911	$ 2,139	1,590,185	(2,095)	(1,403,453)	(802)	(1,063)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)		139
Exercise of stock options, net	1,963	$ 1	1,962
Stock-based compensation (in shares)		58
Stock-based compensation	7,250	$ 1	7,249
Net proceeds from equity offering (in shares)		16,947
Issuance of common stock in public offering, net	464,593	$ 170	464,423
Other comprehensive income (loss)	7					7	0
Net loss	(66,497)				(66,466)		(31)
Ending balance (in shares) at Jun. 30, 2020		231,073
Ending Balance at Jun. 30, 2020	$ 592,227	$ 2,311	$ 2,063,819	$ (2,095)	$ (1,469,919)	$ (795)	$ (1,094)