CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common stock	Additional paid-in capital	Accumulated deficit	Accumulated other comprehensive gain (loss)
Balance (in shares) at Dec. 31, 2018		109,018
Balance at Dec. 31, 2018	$ 1,012,112	$ 109	$ 1,226,588	$ (204,294)	$ (10,291)
Increase (Decrease) in Stockholders' Equity
Net loss	(80,887)			(80,887)
Foreign currency translation adjustment	(2,270)				(2,270)
Unrealized gain on marketable securities, net of tax	101				101
Issuance of common stock upon exercise of options, equity stock and stock units, and employee stock purchase plan (in shares)		2,475
Issuance of common stock upon exercise of options, equity stock and employee stock purchase plan	6,101	$ 2	6,099
Stock-based compensation	21,657		21,657
Cumulative effect adjustment from adoption of new accounting pronouncement | Cumulative effect adjustment from adoption of ASC 842	4,469			4,469
Balance (in shares) at Sep. 30, 2019		111,493
Balance at Sep. 30, 2019	961,283	$ 111	1,254,344	(280,712)	(12,460)
Balance (in shares) at Jun. 30, 2019		111,127
Balance at Jun. 30, 2019	973,226	$ 111	1,246,877	(263,381)	(10,381)
Increase (Decrease) in Stockholders' Equity
Net loss	(17,331)			(17,331)
Foreign currency translation adjustment	(2,096)				(2,096)
Unrealized gain on marketable securities, net of tax	17				17
Issuance of common stock upon exercise of options, equity stock and stock units, and employee stock purchase plan (in shares)		366
Issuance of common stock upon exercise of options, equity stock and employee stock purchase plan	79	$ 0	79
Stock-based compensation	7,388		7,388
Balance (in shares) at Sep. 30, 2019		111,493
Balance at Sep. 30, 2019	961,283	$ 111	1,254,344	(280,712)	(12,460)
Balance (in shares) at Dec. 31, 2019		112,131
Balance at Dec. 31, 2019	970,918	$ 112	1,261,142	(290,244)	(92)
Increase (Decrease) in Stockholders' Equity
Net loss	(31,543)			(31,543)
Foreign currency translation adjustment	8				8
Unrealized gain on marketable securities, net of tax	(48)				(48)
Issuance of common stock upon exercise of options, equity stock and stock units, and employee stock purchase plan (in shares)		1,792
Issuance of common stock upon exercise of options, equity stock and employee stock purchase plan	(702)	$ 2	(704)
Stock-based compensation	19,613		19,613
Balance (in shares) at Sep. 30, 2020		113,923
Balance at Sep. 30, 2020	958,246	$ 114	1,280,051	(321,787)	(132)
Balance (in shares) at Jun. 30, 2020		113,744
Balance at Jun. 30, 2020	965,190	$ 114	1,274,136	(309,008)	(52)
Increase (Decrease) in Stockholders' Equity
Net loss	(12,779)			(12,779)
Foreign currency translation adjustment	6				6
Unrealized gain on marketable securities, net of tax	(86)				(86)
Issuance of common stock upon exercise of options, equity stock and stock units, and employee stock purchase plan (in shares)		179
Issuance of common stock upon exercise of options, equity stock and employee stock purchase plan	(919)	$ 0	(919)
Stock-based compensation	6,834		6,834
Balance (in shares) at Sep. 30, 2020		113,923
Balance at Sep. 30, 2020	$ 958,246	$ 114	$ 1,280,051	$ (321,787)	$ (132)