Condensed Consolidated Statement of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock and Additional Paid-in-Capital	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance at Dec. 31, 2018	$ 650,394	$ 3,152,179	$ (150,000)	$ (2,299)	$ (2,349,486)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock for equity awards, net of tax withholdings		3,159
Shares withheld for taxes		0
Issuance of common stock related to employee stock purchase plan		12,315
Shares retired		0	0
Issuance of common stock and assumption of options related to Verodin, Inc. acquisition		121,158
Stock-based compensation		120,701
Unrealized gain (loss) investments				3,376
Net loss	(208,193)
Ending balance at Sep. 30, 2019	702,910	3,409,512	(150,000)	1,077	(2,557,679)
Beginning balance at Jun. 30, 2019	728,770	3,369,984	(150,000)	970	(2,492,184)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock for equity awards, net of tax withholdings		1,665
Shares withheld for taxes		0
Issuance of common stock related to employee stock purchase plan		0
Shares retired		0	0
Issuance of common stock and assumption of options related to Verodin, Inc. acquisition		0
Stock-based compensation		37,863
Unrealized gain (loss) investments				107
Net loss	(65,495)
Ending balance at Sep. 30, 2019	702,910	3,409,512	(150,000)	1,077	(2,557,679)
Beginning balance at Dec. 31, 2019	701,666	3,457,381	(150,000)	1,180	(2,606,895)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock for equity awards, net of tax withholdings		6,270
Shares withheld for taxes		(8,802)
Issuance of common stock related to employee stock purchase plan		12,300
Shares retired		(70,000)	70,000
Issuance of common stock and assumption of options related to Verodin, Inc. acquisition
Stock-based compensation		116,492
Unrealized gain (loss) investments				3,934
Net loss	(168,700)				(168,700)
Ending balance at Sep. 30, 2020	663,160	3,513,641	(80,000)	5,114	(2,775,595)
Beginning balance at Jun. 30, 2020	660,359	3,470,524	(80,000)	6,311	(2,736,477)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock for equity awards, net of tax withholdings		2,539
Shares withheld for taxes		(762)
Issuance of common stock related to employee stock purchase plan		0
Shares retired		0	0
Issuance of common stock and assumption of options related to Verodin, Inc. acquisition		0
Stock-based compensation		41,340
Unrealized gain (loss) investments				(1,197)
Net loss	(39,118)
Ending balance at Sep. 30, 2020	$ 663,160	$ 3,513,641	$ (80,000)	$ 5,114	$ (2,775,595)