Unaudited Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Accumulated other comprehensive income (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]
Stock-based compensation expense	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) gains 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, 2017		28,146,162
Balance at Dec. 31, 2017	114,642	$ 28	223,868	136	(109,390)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Unrealized (losses) gains on derivative instruments	(2,985)
Unrealized (losses) gains on available for sale securities	11
Net loss	(27,729)
Balance at Jun. 30, 2018	103,806	$ 29	243,734	(2,838)	(137,119)
Ending (in shares) at Jun. 30, 2018		29,218,030
Balance (in shares) at Mar. 31, 2018		28,748,631
Balance at Mar. 31, 2018	105,480	$ 29	231,860	(1,973)	(124,436)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	8,848		8,848
Common stock issued under employee stock plans, net (in shares)		469,399
Common stock issued under employee stock plans, net	3,026	$ 0	3,026
Unrealized (losses) gains on derivative instruments	(884)			(884)
Unrealized (losses) gains on available for sale securities	19			19
Net loss	(12,683)				(12,683)
Balance at Jun. 30, 2018	103,806	$ 29	243,734	(2,838)	(137,119)
Ending (in shares) at Jun. 30, 2018		29,218,030
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]
Stock-based compensation expense	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)	$ 0	(4,642)
Unrealized (losses) gains 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
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]
Unrealized (losses) gains on derivative instruments	3,847
Unrealized (losses) gains on available for sale securities	44
Net loss	(47,127)
Balance at Jun. 30, 2019	100,194	$ 30	285,001	258	(185,095)
Ending (in shares) at Jun. 30, 2019		30,327,027
Balance (in shares) at Mar. 31, 2019		30,263,237
Balance at Mar. 31, 2019	109,995	$ 30	271,260	(688)	(160,607)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	14,796		14,796
Common stock issued under employee stock plans, net (in shares)		63,790
Common stock issued under employee stock plans, net	(1,055)	$ 0	(1,055)
Unrealized (losses) gains on derivative instruments	912			912
Unrealized (losses) gains on available for sale securities	34			34
Net loss	(24,488)				(24,488)
Balance at Jun. 30, 2019	$ 100,194	$ 30	$ 285,001	$ 258	$ (185,095)
Ending (in shares) at Jun. 30, 2019		30,327,027