CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Income (Deficit)	Accumulated Other Comprehensive Income (Loss)
Balance, beginning (shares) at Dec. 31, 2016		62,269
Balance, beginning of period at Dec. 31, 2016	$ 1,300	$ 1	$ 252,126	$ (250,535)	$ (292)
Issuance of common stock from exercise of equity awards and employee stock purchase plan (in shares)		1,752
Issuance of common stock from exercise of equity awards and employee stock purchase plan	531		531
Issuance of common stock, net of offering costs (shares)		21,893
Issuance of common stock, net of offering costs	26,425		26,425
Issuance/sale of warrants	1,447		1,447
Stock-based compensation	6,727		6,727
Net income (loss)	(45,192)			(45,192)
Foreign currency translation adjustments	(364)				(364)
Balance, beginning (shares) at Dec. 31, 2017		85,914
Balance, end of period at Dec. 31, 2017	(9,126)	$ 1	287,256	(295,727)	(656)
Issuance of common stock from exercise of equity awards and employee stock purchase plan (in shares)		3,185
Issuance of common stock from exercise of equity awards and employee stock purchase plan	2,806		2,806
Issuance of common stock, net of offering costs (shares)		9,524
Issuance of common stock, net of offering costs	19,766		19,766
Issuance of common stock related to acquisition (shares)		7,500
Issuance of common stock related to acquisition	32,319		32,319
Exercise of warrants (shares)		912
Stock-based compensation	11,188		11,188
Net income (loss)	(11,627)			(11,627)
Foreign currency translation adjustments	1,398				1,398
Balance, beginning (shares) at Dec. 31, 2018		107,035
Balance, end of period at Dec. 31, 2018	7,776	$ 1	353,335	(346,302)	742
Issuance of common stock from exercise of equity awards and employee stock purchase plan (in shares)		5,273
Issuance of common stock from exercise of equity awards and employee stock purchase plan	4,985		4,985
Payment of withholding taxes related to net share settlement of equity awards	(8,198)		(8,198)
Conversion of convertible notes due 2023, net (in shares)		10,801
Conversion of convertible notes due 2023, net	58,857		58,857
Equity component of convertible notes due 2024, net	35,387		35,387
Cost of convertible notes hedge related to the convertible notes due 2024	(36,313)		(36,313)
Issuance/sale of warrants	29,818		29,818
Stock-based compensation	20,417		20,417
Net income (loss)	161,148			161,148
Foreign currency translation adjustments	(1,665)				(1,665)
Balance, beginning (shares) at Dec. 31, 2019		123,109
Balance, end of period at Dec. 31, 2019	$ 272,212	$ 1	$ 458,315	$ (185,181)	$ (923)