CONSOLIDATED STATEMENTS OF CHANGES IN REDEEMABLE CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS’ EQUITY (DEFICIT) - USD ($) $ in Millions	Total	Redeemable Convertible Preferred Stock	Common Stock Class A and Class B Common Stock	Additional Paid-In Capital	Other Comprehensive Income	Accumulated Deficit
Beginning balance (in shares) at Jun. 30, 2018		176,300,000
Beginning balance at Jun. 30, 2018		$ 406.3
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of Series F redeemable convertible preferred stock, net (in shares)		38,100,000
Issuance of Series F redeemable convertible preferred stock, net		$ 539.1
Repurchase of common and preferred stock (in shares)		(3,800,000)
Repurchase of common and preferred stock		$ (4.3)
Ending balance (in shares) at Mar. 31, 2019		210,600,000
Ending balance at Mar. 31, 2019		$ 941.1
Beginning balance (in shares) at Jun. 30, 2018			25,900,000
Beginning balance at Jun. 30, 2018	$ (315.6)		$ 0.0	$ 20.5	$ 0.0	$ (336.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchase of common and preferred stock (in shares)			(4,800,000)
Repurchase of common and preferred stock	(97.8)					(97.8)
Exercise of stock options (in shares)			1,800,000
Exercise of stock options	3.8			3.8
Stock-based compensation expense	48.1			48.1
Other comprehensive income (loss)	1.0				1.0
Net loss	(148.2)					(148.2)
Ending balance (in shares) at Mar. 31, 2019			22,900,000
Ending balance at Mar. 31, 2019	(508.7)		$ 0.0	72.3	1.0	(582.0)
Beginning balance (in shares) at Dec. 31, 2018		210,600,000
Beginning balance at Dec. 31, 2018		$ 941.1
Ending balance (in shares) at Mar. 31, 2019		210,600,000
Ending balance at Mar. 31, 2019		$ 941.1
Beginning balance (in shares) at Dec. 31, 2018			22,100,000
Beginning balance at Dec. 31, 2018	(479.5)		$ 0.0	63.3	0.6	(543.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)			800,000
Exercise of stock options	1.4			1.4
Stock-based compensation expense	7.6			7.6
Other comprehensive income (loss)	0.4				0.4
Net loss	(38.6)					(38.6)
Ending balance (in shares) at Mar. 31, 2019			22,900,000
Ending balance at Mar. 31, 2019	$ (508.7)		$ 0.0	72.3	1.0	(582.0)
Beginning balance (in shares) at Jun. 30, 2019	210,640,629	210,600,000
Beginning balance at Jun. 30, 2019	$ 941.1	$ 941.1
Increase (Decrease) in Temporary Equity [Roll Forward]
Conversion of redeemable convertible preferred stock to common stock (in shares)		(210,600,000)
Conversion of redeemable convertible preferred stock to common stock		$ (941.1)
Ending balance (in shares) at Mar. 31, 2020	0	0
Ending balance at Mar. 31, 2020	$ 0.0	$ 0.0
Beginning balance (in shares) at Jun. 30, 2019			25,300,000
Beginning balance at Jun. 30, 2019	(538.6)		$ 0.0	90.7	0.2	(629.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Initial public offering, net of issuance costs (in shares)			43,400,000
Initial public offering, net of issuance costs	1,195.7			1,195.7
Conversion of redeemable convertible preferred stock to common stock (in shares)			210,600,000
Conversion of redeemable convertible preferred stock to common stock	$ 941.1			941.1
Exercise of stock options (in shares)	2,448,692		2,400,000
Exercise of stock options	$ 11.0			11.0
Issuance of common stock under employee stock purchase plan (in shares)			200,000
Issuance of common stock under employee stock purchase plan	3.7			3.7
Exercise of stock warrants (in shares)			200,000
Stock-based compensation expense	57.8			57.8
Other comprehensive income (loss)	0.1				0.1
Net loss	(160.7)					(160.7)
Ending balance (in shares) at Mar. 31, 2020			282,200,000
Ending balance at Mar. 31, 2020	$ 1,517.3		$ 0.0	2,300.0	0.3	(783.0)
Beginning balance (in shares) at Dec. 31, 2019		0
Beginning balance at Dec. 31, 2019		$ 0.0
Increase (Decrease) in Temporary Equity [Roll Forward]
Conversion of redeemable convertible preferred stock to common stock (in shares)		(210,640,629)
Ending balance (in shares) at Mar. 31, 2020	0	0
Ending balance at Mar. 31, 2020	$ 0.0	$ 0.0
Beginning balance (in shares) at Dec. 31, 2019			280,600,000
Beginning balance at Dec. 31, 2019	1,545.2		$ 0.0	2,269.3	3.3	(727.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)			1,500,000
Exercise of stock options	5.9			5.9
Issuance of common stock under employee stock purchase plan (in shares)			200,000
Issuance of common stock under employee stock purchase plan	3.7			3.7
Stock-based compensation expense	21.1			21.1
Other comprehensive income (loss)	(3.0)				(3.0)
Net loss	(55.6)					(55.6)
Ending balance (in shares) at Mar. 31, 2020			282,200,000
Ending balance at Mar. 31, 2020	$ 1,517.3		$ 0.0	$ 2,300.0	$ 0.3	$ (783.0)