Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Common Stock [Member]		Additional Paid-in Capital [Member]	AOCI Attributable to Parent [Member]	Retained Earnings [Member]	Total
Balance (in shares) at Dec. 31, 2014	24,685,604
Balance at Dec. 31, 2014	$ 25		$ 162,478	$ (326)	$ (67,151)	$ 95,026
Stock-based compensation expense			7,794			$ 7,794
Exercise of stock options (in shares)	1,350,162					1,334,351
Exercise of stock options	$ 1		2,054			$ 2,055
Exercise of restricted stock units (in shares)	33,388
Exercise of restricted stock units		[1]
Unrealized gains (losses) on derivative instruments				(5)		(5)
Net loss					(21,283)	(21,283)
Unrealized losses on short-term investments
Balance (in shares) at Dec. 31, 2015	26,069,154
Balance at Dec. 31, 2015	$ 26		172,326	(331)	(88,434)	83,587
Stock-based compensation expense			12,938			$ 12,938
Exercise of stock options (in shares)						445,535
Unrealized gains (losses) on derivative instruments				(148)		$ (148)
Net loss					(17,710)	(17,710)
Common stock issued under employee stock plans, net (in shares)	752,608
Common stock issued under employee stock plans, net	$ 1		4,071			4,072
Unrealized losses on short-term investments
Balance (in shares) at Dec. 31, 2016	26,821,762
Balance at Dec. 31, 2016	$ 27		189,335	(479)	(106,144)	82,739
Effect of adoption of ASU 2016-09 | Accounting Standards Update 2016-09 [Member]			2,616		(2,616)
Stock-based compensation expense			19,835			$ 19,835
Exercise of stock options (in shares)						832,270
Unrealized gains (losses) on derivative instruments				642		$ 642
Net loss					(13,694)	(13,694)
Common stock issued under employee stock plans, net (in shares)	1,324,400
Common stock issued under employee stock plans, net	$ 1		12,082			12,083
Unrealized losses on short-term investments				(27)		(27)
Balance (in shares) at Dec. 31, 2017	28,146,162
Balance at Dec. 31, 2017	$ 28		$ 223,868	$ 136	$ (122,454)	$ 101,578

[1] Represents an amount lower than $ 1.