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	(63,556)			(63,556)
Foreign currency translation adjustment	(174)				(174)
Unrealized gain on marketable securities, net of tax	84				84
Issuance of common stock upon exercise of options, equity stock and stock units, and employee stock purchase plan (in shares)		2,109
Issuance of common stock upon exercise of options, equity stock and employee stock purchase plan	6,022	$ 2	6,020
Stock-based compensation	14,269		14,269
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 Jun. 30, 2019		111,127
Balance at Jun. 30, 2019	973,226	$ 111	1,246,877	(263,381)	(10,381)
Balance (in shares) at Mar. 31, 2019		110,396
Balance at Mar. 31, 2019	999,887	$ 110	1,234,846	(226,401)	(8,668)
Increase (Decrease) in Stockholders' Equity
Net loss	(36,980)			(36,980)
Foreign currency translation adjustment	(1,749)				(1,749)
Unrealized gain on marketable securities, net of tax	36				36
Issuance of common stock upon exercise of options, equity stock and stock units, and employee stock purchase plan (in shares)		731
Issuance of common stock upon exercise of options, equity stock and employee stock purchase plan	4,952	$ 1	4,951
Stock-based compensation	7,080		7,080
Balance (in shares) at Jun. 30, 2019		111,127
Balance at Jun. 30, 2019	973,226	$ 111	1,246,877	(263,381)	(10,381)
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	(18,764)			(18,764)
Foreign currency translation adjustment	2				2
Unrealized gain on marketable securities, net of tax	38				38
Issuance of common stock upon exercise of options, equity stock and stock units, and employee stock purchase plan (in shares)		1,613
Issuance of common stock upon exercise of options, equity stock and employee stock purchase plan	217	$ 2	215
Stock-based compensation	12,779		12,779
Balance (in shares) at Jun. 30, 2020		113,744
Balance at Jun. 30, 2020	965,190	$ 114	1,274,136	(309,008)	(52)
Balance (in shares) at Mar. 31, 2020		113,275
Balance at Mar. 31, 2020	965,698	$ 113	1,264,000	(298,227)	(188)
Increase (Decrease) in Stockholders' Equity
Net loss	(10,781)			(10,781)
Foreign currency translation adjustment	2				2
Unrealized gain on marketable securities, net of tax	134				134
Issuance of common stock upon exercise of options, equity stock and stock units, and employee stock purchase plan (in shares)		469
Issuance of common stock upon exercise of options, equity stock and employee stock purchase plan	3,430	$ 1	3,429
Stock-based compensation	6,707		6,707
Balance (in shares) at Jun. 30, 2020		113,744
Balance at Jun. 30, 2020	$ 965,190	$ 114	$ 1,274,136	$ (309,008)	$ (52)