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)		1,139,628
Stock issued from exercise of stock options, net	6,760	$ 11	6,749
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)		400,310
Restricted stock tax vesting	(2,555)		(2,555)
Stock issued for contingent consideration (in shares)		771,804
Stock issued for contingent consideration	9,316	$ 8	9,308
Stock-based compensation	22,679		22,679
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	562				562
Foreign currency translation adjustment	77				77
Net loss	(204,850)					(204,850)
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)
Balance (in shares) at Mar. 31, 2019		230,180,714
Balance at Mar. 31, 2019	451,668	$ 2,347	1,970,607	12,387	(1,152)	(1,532,521)
Increase (Decrease) in Stockholders' Equity
Stock issued from exercise of stock options, net (in shares)		561,177
Stock issued from exercise of stock options, net	2,807	$ 5	2,802
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)		99,252
Restricted stock tax vesting	(615)		(615)
Stock-based compensation	9,935		9,935
Equity component of the convertible notes (in shares)		4,951,449
Equity component of the convertible notes	24,718	$ 50	24,668
Termination of capped call confirmations	5,243		5,243
Unrealized holding gain (loss) on available-for-sale securities	(22)				(22)
Foreign currency translation adjustment	1,881				1,881
Net loss	(84,551)					(84,551)
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)
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)		1,609,235
Stock issued from exercise of stock options, net	10,733	$ 16	10,717
Restricted stock tax vesting (in shares)		1,196,738
Restricted stock tax vesting	(8,097)		(8,097)
Stock-based compensation	21,004		21,004
Unrealized holding gain (loss) on available-for-sale securities	248				248
Foreign currency translation adjustment	2,080				2,080
Net loss	$ (141,440)					(141,440)
Balance (in shares) at Jun. 30, 2020	258,223,842	258,223,842
Balance at Jun. 30, 2020	$ 360,953	$ 2,614	2,250,849	12,387	5,153	(1,910,050)
Balance (in shares) at Mar. 31, 2020		257,449,955
Balance at Mar. 31, 2020	402,594	$ 2,607	2,238,346	12,387	6,812	(1,857,558)
Increase (Decrease) in Stockholders' Equity
Stock issued from exercise of stock options, net (in shares)		650,288
Stock issued from exercise of stock options, net	4,656	$ 7	4,649
Restricted stock tax vesting (in shares)		123,599
Restricted stock tax vesting	(554)		(554)
Stock-based compensation	8,408		8,408
Unrealized holding gain (loss) on available-for-sale securities	457				457
Foreign currency translation adjustment	(2,116)				(2,116)
Net loss	$ (52,492)					(52,492)
Balance (in shares) at Jun. 30, 2020	258,223,842	258,223,842
Balance at Jun. 30, 2020	$ 360,953	$ 2,614	$ 2,250,849	$ 12,387	$ 5,153	$ (1,910,050)