Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	0.375%Convertible Senior Notes Due 2025 as Liability Component [Member]	0.25% Convertible Senior Notes Due 2022 as Liability Component [Member]	Common Stock [Member]	Common Stock [Member] 0.25% Convertible Senior Notes Due 2022 as Liability Component [Member]	Treasury Stock [Member]	Additional Paid-In Capital [Member]	Additional Paid-In Capital [Member] 0.375%Convertible Senior Notes Due 2025 as Liability Component [Member]	Additional Paid-In Capital [Member] 0.25% Convertible Senior Notes Due 2022 as Liability Component [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Beginning Balance, Amount at Dec. 31, 2018	$ 244,641			$ 40			$ 589,708			$ (723)	$ (344,384)
Beginning Balance, Shares at Dec. 31, 2018				39,300
Issuance of common stock under stock plans, net of shares withheld for employee taxes	16,861			$ 2			16,859
Issuance of common stock under stock plans, net of shares withheld for employee taxes, Shares				1,504
Stock-based compensation	99,185						99,185
Issuance of common stock in relation to common stock offering, net of offering costs incurred $365	342,630			$ 2			342,628
Issuance of common stock in relation to common stock offering, net of offering costs incurred $365, Shares				2,151
Cumulative translation adjustment	(213)									(213)
Unrealized gain on investments, net of income taxes of 156, ($116) and ($44)	600									600
Net loss	(53,746)										(53,746)
Ending Balance, Amount at Dec. 31, 2019	649,958			$ 44			1,048,380			(336)	(398,130)
Ending Balance, Shares at Dec. 31, 2019				42,955
Issuance of common stock under stock plans, net of shares withheld for employee taxes	22,174						22,174
Issuance of common stock under stock plans, net of shares withheld for employee taxes, Shares				1,565
Equity component of notes payable, net of issuance costs & repayment		$ 96,610	$ 613		$ 2			$ 96,610	$ 611
Equity component of notes payable, net of issuance costs & repayment, Shares					1,595
Purchase of Capped Call Options	(50,600)						(50,600)
Stock-based compensation	123,102						123,102
Equity component of the 2022 Notes conversion			(172)						(172)
Settlement of Convertible Note Hedges	1,062						1,062
Settlement of Convertible Note Hedges, Shares						12
Cumulative translation adjustment	4,790									4,790
Unrealized gain on investments, net of income taxes of 156, ($116) and ($44)	149									149
Net loss	(85,031)										(85,031)
Ending Balance, Amount at Dec. 31, 2020	762,655			$ 46			1,241,167			4,603	(483,161)
Ending Balance, Shares at Dec. 31, 2020				46,115		12
Issuance of common stock under stock plans, net of shares withheld for employee taxes	27,489			$ 1			27,488
Issuance of common stock under stock plans, net of shares withheld for employee taxes, Shares				1,275
Stock-based compensation	169,727						169,727
Equity component of the 2022 Notes conversion			$ (11,277)		$ 1				$ (11,278)
Equity component of the 2022 Notes conversions, Shares					898
Settlement of Convertible Note Hedges	8,984			$ (1)			8,985
Settlement of Convertible Note Hedges, Shares				(898)		898
Cumulative translation adjustment	(4,712)									(4,712)
Unrealized gain on investments, net of income taxes of 156, ($116) and ($44)	(1,230)									(1,230)
Net loss	(77,837)										(77,837)
Ending Balance, Amount at Dec. 31, 2021	$ 873,799			$ 47			$ 1,436,089			$ (1,339)	$ (560,998)
Ending Balance, Shares at Dec. 31, 2021				47,390		910