Redeemable Convertible Preferred Stock - Schedule of Convertible Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Redeemable convertible preferred stock, shares authorized (in shares)	0	227,328,900
Redeemable convertible preferred stock, shares issued (in shares)	0	219,175,709
Redeemable convertible preferred stock, shares outstanding (in shares)	0	219,175,709
Redeemable convertible preferred stock, liquidation preference		$ 5,161,947
Redeemable convertible preferred stock, carrying value	$ 0	$ 5,152,047
Series Seed
Class of Stock [Line Items]
Redeemable convertible preferred stock, shares authorized (in shares)		6,063,921
Redeemable convertible preferred stock, shares issued (in shares)		6,063,921
Redeemable convertible preferred stock, shares outstanding (in shares)		6,063,921
Redeemable convertible preferred stock, issue price (in dollars per share)		$ 0.23
Redeemable convertible preferred stock, per conversion price (in dollars per share)		$ 0.23
Redeemable convertible preferred stock, liquidation preference		$ 1,365
Redeemable convertible preferred stock, carrying value		$ 1,332
Series A
Class of Stock [Line Items]
Redeemable convertible preferred stock, shares authorized (in shares)		8,129,364
Redeemable convertible preferred stock, shares issued (in shares)		8,129,364
Redeemable convertible preferred stock, shares outstanding (in shares)		8,129,364
Redeemable convertible preferred stock, issue price (in dollars per share)		$ 0.76
Redeemable convertible preferred stock, per conversion price (in dollars per share)		$ 0.76
Redeemable convertible preferred stock, liquidation preference		$ 6,200
Redeemable convertible preferred stock, carrying value		$ 6,180
Series B
Class of Stock [Line Items]
Redeemable convertible preferred stock, shares authorized (in shares)		7,067,771
Redeemable convertible preferred stock, shares issued (in shares)		7,067,771
Redeemable convertible preferred stock, shares outstanding (in shares)		7,067,771
Redeemable convertible preferred stock, issue price (in dollars per share)		$ 2.10
Redeemable convertible preferred stock, per conversion price (in dollars per share)		$ 2.10
Redeemable convertible preferred stock, liquidation preference		$ 14,860
Redeemable convertible preferred stock, carrying value		$ 14,794
Series C
Class of Stock [Line Items]
Redeemable convertible preferred stock, shares authorized (in shares)		14,479,445
Redeemable convertible preferred stock, shares issued (in shares)		14,479,445
Redeemable convertible preferred stock, shares outstanding (in shares)		14,479,445
Redeemable convertible preferred stock, issue price (in dollars per share)		$ 4.25
Redeemable convertible preferred stock, per conversion price (in dollars per share)		$ 4.25
Redeemable convertible preferred stock, liquidation preference		$ 61,500
Redeemable convertible preferred stock, carrying value		$ 61,440
Series D
Class of Stock [Line Items]
Redeemable convertible preferred stock, shares authorized (in shares)		24,674,534
Redeemable convertible preferred stock, shares issued (in shares)		24,674,534
Redeemable convertible preferred stock, shares outstanding (in shares)		24,674,534
Redeemable convertible preferred stock, issue price (in dollars per share)		$ 10.13
Redeemable convertible preferred stock, per conversion price (in dollars per share)		$ 10.13
Redeemable convertible preferred stock, liquidation preference		$ 250,000
Redeemable convertible preferred stock, carrying value		$ 249,878
Series E
Class of Stock [Line Items]
Redeemable convertible preferred stock, shares authorized (in shares)		47,099,094
Redeemable convertible preferred stock, shares issued (in shares)		47,099,094
Redeemable convertible preferred stock, shares outstanding (in shares)		47,099,094
Redeemable convertible preferred stock, issue price (in dollars per share)		$ 19.45
Redeemable convertible preferred stock, per conversion price (in dollars per share)		$ 19.45
Redeemable convertible preferred stock, liquidation preference		$ 915,870
Redeemable convertible preferred stock, carrying value		$ 913,810
Series F
Class of Stock [Line Items]
Redeemable convertible preferred stock, shares authorized (in shares)		37,263,568
Redeemable convertible preferred stock, shares issued (in shares)		37,263,568
Redeemable convertible preferred stock, shares outstanding (in shares)		37,263,568
Redeemable convertible preferred stock, issue price (in dollars per share)		$ 26.79
Redeemable convertible preferred stock, per conversion price (in dollars per share)		$ 26.79
Redeemable convertible preferred stock, liquidation preference		$ 998,250
Redeemable convertible preferred stock, carrying value		$ 991,336
Series G
Class of Stock [Line Items]
Redeemable convertible preferred stock, shares authorized (in shares)		18,662,127
Redeemable convertible preferred stock, shares issued (in shares)		18,662,127
Redeemable convertible preferred stock, shares outstanding (in shares)		18,662,127
Redeemable convertible preferred stock, issue price (in dollars per share)		$ 32.15
Redeemable convertible preferred stock, per conversion price (in dollars per share)		$ 32.15
Redeemable convertible preferred stock, liquidation preference		$ 599,987
Redeemable convertible preferred stock, carrying value		$ 599,715
Series H
Class of Stock [Line Items]
Redeemable convertible preferred stock, shares authorized (in shares)		42,771,492
Redeemable convertible preferred stock, shares issued (in shares)		42,771,492
Redeemable convertible preferred stock, shares outstanding (in shares)		42,771,492
Redeemable convertible preferred stock, issue price (in dollars per share)		$ 39.75
Redeemable convertible preferred stock, per conversion price (in dollars per share)		$ 39.75
Redeemable convertible preferred stock, liquidation preference		$ 1,700,000
Redeemable convertible preferred stock, carrying value		$ 1,699,726
Series I
Class of Stock [Line Items]
Redeemable convertible preferred stock, shares authorized (in shares)		21,117,584
Redeemable convertible preferred stock, shares issued (in shares)		12,964,393
Redeemable convertible preferred stock, shares outstanding (in shares)		12,964,393
Redeemable convertible preferred stock, issue price (in dollars per share)		$ 47.35
Redeemable convertible preferred stock, per conversion price (in dollars per share)		$ 47.35
Redeemable convertible preferred stock, liquidation preference		$ 613,915
Redeemable convertible preferred stock, carrying value		$ 613,836
Redeemable Convertible Preferred Stock
Class of Stock [Line Items]
Redeemable convertible preferred stock, shares outstanding (in shares)	0	219,176,000	199,815,000	144,778,000
Redeemable convertible preferred stock, carrying value	$ 0	$ 5,152,047	$ 4,284,049	$ 2,238,770