Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Accumulated other comprehensive loss	Accumulated deficit
Balance (in shares) at Dec. 31, 2017		28,146,162
Balance at Dec. 31, 2017	$ 114,642	$ 28	$ 223,868	$ 136	$ (109,390)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued under employee stock plans, net	6,927		6,927
Common stock issued under employee stock plans, net (in shares)		602,469
Common stock issued under employee stock plans, net	1,066	$ 1	1,065
Unrealized losses on derivative instruments	(2,101)			(2,101)
Unrealized (losses) gains on available for sale securities	(8)			(8)
Net loss	(15,046)				(15,046)
Balance at Mar. 31, 2018	105,480	$ 29	231,860	(1,973)	(124,436)
Ending (in shares) at Mar. 31, 2018		28,748,631
Balance (in shares) at Dec. 31, 2018		29,576,880
Balance at Dec. 31, 2018	125,370	$ 30	266,941	(3,633)	(137,968)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued under employee stock plans, net	8,961		8,961
Common stock issued under employee stock plans, net (in shares)		686,357
Common stock issued under employee stock plans, net	(4,642)		(4,642)
Unrealized losses on derivative instruments	2,935			2,935
Unrealized (losses) gains on available for sale securities	10			10
Net loss	(22,639)				(22,639)
Balance at Mar. 31, 2019	$ 109,995	$ 30	$ 271,260	$ (688)	$ (160,607)
Ending (in shares) at Mar. 31, 2019		30,263,237