Condensed Consolidated Statements of Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Additional Paid-In Capital	Additional Paid-In Capital Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Accumulated Deficit Cumulative Effect, Period of Adoption, Adjustment
Beginning Balance (in shares) at Dec. 31, 2020			93.5
Beginning Balance at Dec. 31, 2020	$ 1,126.2		$ 0.1	$ 1,849.7		$ 1.8	$ (725.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	74.4						74.4
Unrealized loss on debt securities available-for-sale, net of tax	(1.1)					(1.1)
Stock-based compensation expense	61.5			61.5
Issuances of common stock under stock plans (in shares)			1.1
Issuances of common stock under stock plans	18.2			18.2
Ending Balance (in shares) at Jun. 30, 2021			94.6
Ending Balance at Jun. 30, 2021	1,279.2		$ 0.1	1,929.4		0.7	(651.0)
Beginning Balance (in shares) at Mar. 31, 2021			94.5
Beginning Balance at Mar. 31, 2021	1,205.6		$ 0.1	1,897.8		1.0	(693.3)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	42.3						42.3
Unrealized loss on debt securities available-for-sale, net of tax	(0.3)					(0.3)
Stock-based compensation expense	28.6			28.6
Issuances of common stock under stock plans (in shares)			0.1
Issuances of common stock under stock plans	3.0			3.0
Ending Balance (in shares) at Jun. 30, 2021			94.6
Ending Balance at Jun. 30, 2021	1,279.2		$ 0.1	1,929.4		0.7	(651.0)
Beginning Balance (in shares) at Dec. 31, 2021			94.9
Beginning Balance at Dec. 31, 2021	1,374.0	$ (32.3)	$ 0.1	2,011.4	$ (106.8)	(1.7)	(635.8)	$ 74.5
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(3.0)						(3.0)
Unrealized loss on debt securities available-for-sale, net of tax	(10.5)					(10.5)
Stock-based compensation expense	86.5			86.5
Issuances of common stock under stock plans (in shares)			0.7
Issuances of common stock under stock plans	8.7			8.7
Ending Balance (in shares) at Jun. 30, 2022			95.6
Ending Balance at Jun. 30, 2022	1,423.4		$ 0.1	1,999.8		(12.2)	(564.3)
Beginning Balance (in shares) at Mar. 31, 2022			95.5
Beginning Balance at Mar. 31, 2022	1,391.1		$ 0.1	1,947.7		(9.3)	(547.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(16.9)						(16.9)
Unrealized loss on debt securities available-for-sale, net of tax	(2.9)					(2.9)
Stock-based compensation expense	49.5			49.5
Issuances of common stock under stock plans (in shares)			0.1
Issuances of common stock under stock plans	2.6			2.6
Ending Balance (in shares) at Jun. 30, 2022			95.6
Ending Balance at Jun. 30, 2022	$ 1,423.4		$ 0.1	$ 1,999.8		$ (12.2)	$ (564.3)