Unaudited Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Accumulated other comprehensive income	Accumulated deficit
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)
Realized and unrealized income on derivative instruments	2,935			2,935
Unrealized gains (losses) on available for sale securities	10			10
Net loss	(22,639)				(22,639)
Ending (in shares) at Mar. 31, 2019		30,263,237
Balance at Mar. 31, 2019	109,995	$ 30	271,260	(688)	(160,607)
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]
Realized and unrealized income on derivative instruments	4,369
Unrealized gains (losses) on available for sale securities	35
Net loss	(64,114)
Ending (in shares) at Sep. 30, 2019		30,482,452
Balance at Sep. 30, 2019	97,770	$ 30	299,051	771	(202,082)
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)
Realized and unrealized income on derivative instruments	912			912
Unrealized gains (losses) on available for sale securities	34			34
Net loss	(24,488)				(24,488)
Ending (in shares) at Jun. 30, 2019		30,327,027
Balance at Jun. 30, 2019	100,194	$ 30	285,001	258	(185,095)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	11,022		11,022
Common stock issued under employee stock plans, net (in shares)		155,425
Common stock issued under employee stock plans, net	3,028	$ 0	3,028
Realized and unrealized income on derivative instruments	522			522
Unrealized gains (losses) on available for sale securities	(9)			(9)
Net loss	(16,987)				(16,987)
Ending (in shares) at Sep. 30, 2019		30,482,452
Balance at Sep. 30, 2019	97,770	$ 30	299,051	771	(202,082)
Balance (in shares) at Dec. 31, 2019		30,583,311
Balance at Dec. 31, 2019	93,532	$ 31	310,682	(449)	(216,732)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	12,883		12,883
Common stock issued under employee stock plans, net (in shares)		882,959
Common stock issued under employee stock plans, net	4,316	$ 0	4,316
Realized and unrealized income on derivative instruments	545			545
Unrealized gains (losses) on available for sale securities	195			195
Net loss	(31,430)				(31,430)
Ending (in shares) at Mar. 31, 2020		31,466,270
Balance at Mar. 31, 2020	80,041	$ 31	327,881	291	(248,162)
Balance (in shares) at Dec. 31, 2019		30,583,311
Balance at Dec. 31, 2019	93,532	$ 31	310,682	(449)	(216,732)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Realized and unrealized income on derivative instruments	4,112
Unrealized gains (losses) on available for sale securities	2
Net loss	(74,978)
Ending (in shares) at Sep. 30, 2020		31,725,314
Balance at Sep. 30, 2020	82,920	$ 32	370,933	3,665	(291,710)
Balance (in shares) at Mar. 31, 2020		31,466,270
Balance at Mar. 31, 2020	80,041	$ 31	327,881	291	(248,162)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	17,623		17,623
Common stock issued under employee stock plans, net (in shares)		77,249
Common stock issued under employee stock plans, net	498	$ 1	497
Realized and unrealized income on derivative instruments	3,367			3,367
Unrealized gains (losses) on available for sale securities	(122)			(122)
Purchase of capped calls related to Convertible senior notes	(29,348)		(29,348)
Equity component of Convertible senior notes, net	30,794		30,794
Net loss	(24,323)				(24,323)
Ending (in shares) at Jun. 30, 2020		31,543,519
Balance at Jun. 30, 2020	78,530	$ 32	347,447	3,536	(272,485)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	18,678		18,678
Common stock issued under employee stock plans, net (in shares)		181,795
Common stock issued under employee stock plans, net	4,808	$ 0	4,808
Realized and unrealized income on derivative instruments	200			200
Unrealized gains (losses) on available for sale securities	(71)			(71)
Net loss	(19,225)				(19,225)
Ending (in shares) at Sep. 30, 2020		31,725,314
Balance at Sep. 30, 2020	$ 82,920	$ 32	$ 370,933	$ 3,665	$ (291,710)