Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Warrants	Other Comprehensive Gain (Loss)	Accumulated Deficit
Balance (in shares) at Dec. 31, 2018		189,383,924
Balance at Dec. 31, 2018	$ 342,912	$ 1,942	$ 1,740,061	$ 13,063	$ 68	$ (1,412,222)
Increase (Decrease) in Stockholders' Equity
Stock issued from exercise of stock options, net (in shares)		1,352,623
Stock issued from exercise of stock options, net	7,808	$ 13	7,795
Stock issued from equity financing (in shares)		18,720,930
Stock issued from equity financing	188,994	$ 187	188,807
Restricted stock tax vesting (in shares)		445,956
Restricted stock tax vesting	(3,001)		(3,001)
Stock issued for contingent consideration (in shares)		771,804
Stock issued for contingent consideration	9,316	$ 8	9,308
Stock-based compensation	31,522		31,522
Warrants exercised (in shares)		101,787
Warrants exercised	812	$ 1	1,487	(676)
Equity component of the convertible notes (in shares)		43,995,139
Equity component of the convertible notes	215,476	$ 440	215,036
Termination of capped call confirmations	19,875		19,875
Unrealized holding gain (loss) on available-for-sale securities	551				551
Foreign currency translation adjustment	661				661
Net loss	(266,659)					(266,659)
Balance (in shares) at Sep. 30, 2019		254,772,163
Balance at Sep. 30, 2019	548,267	$ 2,591	2,210,890	12,387	1,280	(1,678,881)
Balance (in shares) at Jun. 30, 2019		254,513,522
Balance at Jun. 30, 2019	600,058	$ 2,589	2,201,447	12,387	707	(1,617,072)
Increase (Decrease) in Stockholders' Equity
Stock issued from exercise of stock options, net (in shares)		212,995
Stock issued from exercise of stock options, net	1,048	$ 2	1,046
Restricted stock tax vesting (in shares)		45,646
Restricted stock tax vesting	(446)		(446)
Stock-based compensation	8,843		8,843
Unrealized holding gain (loss) on available-for-sale securities	(11)				(11)
Foreign currency translation adjustment	584				584
Net loss	(61,809)					(61,809)
Balance (in shares) at Sep. 30, 2019		254,772,163
Balance at Sep. 30, 2019	$ 548,267	$ 2,591	2,210,890	12,387	1,280	(1,678,881)
Balance (in shares) at Dec. 31, 2019	255,417,869	255,417,869
Balance at Dec. 31, 2019	$ 476,425	$ 2,598	2,227,225	12,387	2,825	(1,768,610)
Increase (Decrease) in Stockholders' Equity
Stock issued from exercise of stock options, net (in shares)		2,832,310
Stock issued from exercise of stock options, net	20,028	$ 28	20,000
Restricted stock tax vesting (in shares)		1,350,471
Restricted stock tax vesting	(9,340)		(9,340)
Stock-based compensation	36,912		36,912
Unrealized holding gain (loss) on available-for-sale securities	(96)				(96)
Foreign currency translation adjustment	1,791				1,791
Net loss	$ (205,451)					(205,451)
Balance (in shares) at Sep. 30, 2020	259,600,650	259,600,650
Balance at Sep. 30, 2020	$ 320,269	$ 2,626	2,274,797	12,387	4,520	(1,974,061)
Balance (in shares) at Jun. 30, 2020		258,223,842
Balance at Jun. 30, 2020	360,953	$ 2,614	2,250,849	12,387	5,153	(1,910,050)
Increase (Decrease) in Stockholders' Equity
Stock issued from exercise of stock options, net (in shares)		1,223,075
Stock issued from exercise of stock options, net	9,295	$ 12	9,283
Restricted stock tax vesting (in shares)		153,733
Restricted stock tax vesting	(1,243)		(1,243)
Stock-based compensation	15,908		15,908
Unrealized holding gain (loss) on available-for-sale securities	(344)				(344)
Foreign currency translation adjustment	(289)				(289)
Net loss	$ (64,011)					(64,011)
Balance (in shares) at Sep. 30, 2020	259,600,650	259,600,650
Balance at Sep. 30, 2020	$ 320,269	$ 2,626	$ 2,274,797	$ 12,387	$ 4,520	$ (1,974,061)