Consolidated Statements of Changes in Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common stock	Additional paid-in capital	Accumulated other comprehensive	Accumulated deficit
Effect of adoption of ASU | Accounting Standards Update 2014-09	$ 9,697				$ 9,697
Balance (in shares) at Dec. 31, 2015		26,069
Balance at Dec. 31, 2015	83,587	$ 26	$ 172,326	$ (331)	(88,434)
Stock-based compensation expense	12,938		12,938
Common stock issued under employee stock plans, net (in shares)		753
Common stock issued under employee stock plans, net	4,072	$ 1	4,071
Unrealized gain (loss) on derivative instruments	(148)			(148)
Unrealized gains and losses on available for sale securities	0
Net loss	(14,193)				(14,193)
Net loss | Accounting Standards Update 2014-09	(14,193)
Balance (in shares) at Dec. 31, 2016		26,822
Balance at Dec. 31, 2016	95,953	$ 27	189,335	(479)	(92,930)
Effect of adoption of ASU | Accounting Standards Update 2016-09	0		2,616		(2,616)
Stock-based compensation expense	19,835		19,835
Common stock issued under employee stock plans, net (in shares)		1,324
Common stock issued under employee stock plans, net	12,083	$ 1	12,082
Unrealized gain (loss) on derivative instruments	642			642
Unrealized gains and losses on available for sale securities	(27)			(27)
Net loss	(13,844)				(13,844)
Net loss | Accounting Standards Update 2014-09	(13,844)
Balance (in shares) at Dec. 31, 2017		28,146
Balance at Dec. 31, 2017	114,642	$ 28	223,868	136	(109,390)
Stock-based compensation expense	34,961		34,961
Common stock issued under employee stock plans, net (in shares)		1,431
Common stock issued under employee stock plans, net	8,114	$ 2	8,112
Unrealized gain (loss) on derivative instruments	(3,790)			(3,790)
Unrealized gains and losses on available for sale securities	21			21
Net loss	(28,578)				(28,578)
Balance (in shares) at Dec. 31, 2018		29,577
Balance at Dec. 31, 2018	$ 125,370	$ 30	$ 266,941	$ (3,633)	$ (137,968)