Statements of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Accumulated other comprehensive gain	Accumulated deficit	Restricted stock units	Restricted stock units Common stock	Restricted stock units Additional paid-in capital	Convertible Debt Convertible Senior Notes At 1.50%, Option Portion
Balance (shares) at Dec. 31, 2016		27,568,103
Balance at Dec. 31, 2016	$ 119,146	$ 8	$ 230,605	$ (69)	$ (111,398)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in a public offering		$ 1
Exercise of stock options (shares)		1,085,041
Exercise of stock options	7,917		7,916
Vested, Number of Shares							599,440
RSUs released net of shares withheld for tax settlement						$ (8,990)		$ (8,990)
ESPP, Shares Purchased for Award		159,532
Stock Issued During Period, Value, Employee Stock Purchase Plan	2,750		2,750
Effect of change in accounting principle related to stock-based compensation	0		377		(377)
Employee stock-based compensation expense	18,196		18,196
Net loss	(10,897)				(10,897)
Other comprehensive income	(122)			(122)
Balance (shares) at Dec. 31, 2017		29,412,116
Balance at Dec. 31, 2017	128,000	$ 9	250,854	(191)	(122,672)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in a public offering		$ 0
Exercise of stock options (shares)		531,788
Exercise of stock options	7,334		7,334
RSUs released net of shares withheld for tax settlement	$ (10,082)							(10,082)
ESPP, Shares Purchased for Award	157,426	157,426
Stock Issued During Period, Value, Employee Stock Purchase Plan	$ 3,270		3,270
Issuance of restricted stock awards							606,808
Employee stock-based compensation expense	20,964		20,964
Net loss	(9,674)				(9,674)
Other comprehensive income	(252)			(252)
Balance (shares) at Dec. 31, 2018		30,708,138
Balance at Dec. 31, 2018	162,867	$ 9	295,647	(443)	(132,346)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Carrying amount of equity component, net of capped calls									$ 23,307
Equity component of convertible senior notes, net					0
Exercise of stock options (shares)		187,174
Exercise of stock options	2,439		2,439
Vested, Number of Shares						978,785
RSUs released net of shares withheld for tax settlement	$ (11,460)							$ (11,460)
ESPP, Shares Purchased for Award	155,373	155,373
Stock Issued During Period, Value, Employee Stock Purchase Plan	$ 3,472		3,472
Issuance of restricted stock awards							610,024
Employee stock-based compensation expense	23,865		23,865
Net loss	(17,980)				(17,980)
Other comprehensive income	622
Balance (shares) at Dec. 31, 2019		31,660,709
Balance at Dec. 31, 2019	163,825	$ 9	$ 313,963	$ 179	$ (150,326)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other Comprehensive Income (Loss), Net of Tax	$ 622
Carrying amount of equity component, net of capped calls									$ 23,307