Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands		Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance (in share) at Dec. 31, 2016			53,363
Beginning balance at Dec. 31, 2016		$ 30,328	$ 53	$ 196,555		$ (166,280)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options and warrants (in shares)			2,033
Issuance of common stock upon exercise of stock options and warrants		6,035	$ 2	6,033
Issuance of common stock upon vesting of restricted stock units (in shares)			971
Issuance of common stock upon vesting of restricted stock units		0	$ 1	(1)
Issuance of common stock under ESPP (in shares)			265
Issuance of common stock under ESPP		4,101	$ 1	4,100
Stock-based compensation		15,343		15,343
Other	[1]	0		172		(172)
Other comprehensive income (loss)		0
Net loss		(8,969)				(8,969)
Ending balance (in shares) at Dec. 31, 2017			56,632
Ending balance at Dec. 31, 2017		46,838	$ 57	222,202	$ 0	(175,421)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity component of issuance of convertible senior notes		30,346		30,346
Issuance of common stock upon exercise of stock options and warrants (in shares)			1,285
Issuance of common stock upon exercise of stock options and warrants		7,779	$ 1	7,778
Issuance of common stock upon vesting of restricted stock units (in shares)			1,047
Issuance of common stock upon vesting of restricted stock units		0	$ 1	(1)
Issuance of common stock under ESPP (in shares)			246
Issuance of common stock under ESPP		5,730	$ 0	5,730
Stock-based compensation		28,484		28,484
Shares held for tax withholdings		(260)		(260)
Other comprehensive income (loss)		(93)			(93)
Net loss		(221)
Ending balance (in shares) at Dec. 31, 2018			59,210
Ending balance at Dec. 31, 2018		142,748	$ 59	294,279	(93)	(151,497)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)			932
Issuance of common stock upon exercise of stock options		7,705	$ 1	7,704
Issuance of common stock upon vesting of restricted stock units (in shares)			1,204
Issuance of common stock upon vesting of restricted stock units		0	$ 1	(1)
Issuance of common stock under ESPP (in shares)			198
Issuance of common stock under ESPP		7,823	$ 0	7,823
Stock-based compensation		42,065		42,065
Other comprehensive income (loss)		669			669
Net loss		(4,552)				(4,552)
Ending balance (in shares) at Dec. 31, 2019			61,544
Ending balance at Dec. 31, 2019		$ 196,458	$ 61	$ 351,870	$ 576	$ (156,049)

[1] Effective January 2017, the Company adopted Accounting Standards Update (“ASU”) 2016-09 - Improvements to Employee Share-Based Payment Accounting. Accordingly, the Company accounted for forfeitures as they occurred rather than by estimating expected forfeitures. This amount represents the net effect of this change. See Note 1 for more information.