Changes in Stockholders' Equity - Summary of Changes in Stockholders' Equity (Detail) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Class Of Stock [Line Items]
Beginning Balance, Amount	$ 762,655	$ 649,958
Issuance of common stock under stock plans, net of shares withheld for employee taxes	6,583	1,320
Stock-based compensation	32,947	27,905
Settlement of Convertible Note Hedges	724
Cumulative translation adjustment	(2,489)	(1,077)
Unrealized gain (loss) on investments, net of income taxes of ($36) and $0	(240)	583
Net loss	(23,159)	(17,716)
Ending Balance, Amount	774,714	660,973
0.25% Convertible Senior Notes Due 2022 as Liability Component [Member]
Class Of Stock [Line Items]
Equity component of the 2022 Notes conversions	(2,307)
Common Stock [Member]
Class Of Stock [Line Items]
Beginning Balance, Amount	$ 46	$ 44
Beginning Balance, Shares	46,115	42,955
Issuance of common stock under stock plans, net of shares withheld for employee taxes	$ 1
Issuance of common stock under stock plans, net of shares withheld for employee taxes, Shares	482	411
Settlement of Convertible Note Hedges, Shares	(364)
Ending Balance, Amount	$ 47	$ 44
Ending Balance, Shares	46,596	43,366
Common Stock [Member] | 0.25% Convertible Senior Notes Due 2022 as Liability Component [Member]
Class Of Stock [Line Items]
Equity component of the 2022 Notes conversions, Shares	363
Treasury Stock [Member]
Class Of Stock [Line Items]
Beginning Balance, Shares	12
Settlement of Convertible Note Hedges, Shares	364
Ending Balance, Shares	376
Additional Paid-In Capital [Member]
Class Of Stock [Line Items]
Beginning Balance, Amount	$ 1,241,167	$ 1,048,380
Issuance of common stock under stock plans, net of shares withheld for employee taxes	6,582	1,320
Stock-based compensation	32,947	27,905
Settlement of Convertible Note Hedges	724
Ending Balance, Amount	1,279,113	1,077,605
Additional Paid-In Capital [Member] | 0.25% Convertible Senior Notes Due 2022 as Liability Component [Member]
Class Of Stock [Line Items]
Equity component of the 2022 Notes conversions	(2,307)
Accumulated Other Comprehensive Income (Loss) [Member]
Class Of Stock [Line Items]
Beginning Balance, Amount	4,603	(336)
Cumulative translation adjustment	(2,489)	(1,077)
Unrealized gain (loss) on investments, net of income taxes of ($36) and $0	(240)	583
Ending Balance, Amount	1,874	(830)
Accumulated Deficit [Member]
Class Of Stock [Line Items]
Beginning Balance, Amount	(483,161)	(398,130)
Net loss	(23,159)	(17,716)
Ending Balance, Amount	$ (506,320)	$ (415,846)