Stockholders’ Equity (Deficit) and Convertible Preferred Stock (Details) - $ / shares	May 06, 2019	Jun. 29, 2019	Mar. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Common stock, authorized (in shares)	500,000,000	500,000,000		58,669,600
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001		$ 0.0001
Convertible preferred stock, authorized (in shares)				43,882,867
Convertible preferred stock, par value (in shares)				$ 0.0001
Common stock, issued (in shares)		60,167,521		6,951,350
Common stock, outstanding (in shares)		60,167,521		6,951,350
Convertible preferred stock, outstanding (in shares)		0	41,562,111	41,562,111	39,486,895	39,474,156	39,361,211
Series A
Class of Stock [Line Items]
Convertible preferred stock, authorized (in shares)		0		3,333,500
Convertible preferred stock, par value (in shares)		$ 0.0001		$ 0.0001
Convertible preferred stock, issued (in shares)		0		3,333,500
Convertible preferred stock, outstanding (in shares)		0		3,333,500
Series B
Class of Stock [Line Items]
Convertible preferred stock, authorized (in shares)		0		4,802,260
Convertible preferred stock, par value (in shares)		$ 0.0001		$ 0.0001
Convertible preferred stock, issued (in shares)		0		4,680,565
Convertible preferred stock, outstanding (in shares)		0		4,680,565
Series C
Class of Stock [Line Items]
Convertible preferred stock, authorized (in shares)		0		8,076,643
Convertible preferred stock, par value (in shares)		$ 0.0001		$ 0.0001
Convertible preferred stock, issued (in shares)		0		8,076,636
Convertible preferred stock, outstanding (in shares)		0		8,076,636
Series D
Class of Stock [Line Items]
Convertible preferred stock, authorized (in shares)		0		8,713,207
Convertible preferred stock, par value (in shares)		$ 0.0001		$ 0.0001
Convertible preferred stock, issued (in shares)		0		8,713,201
Convertible preferred stock, outstanding (in shares)		0		8,713,201
Series E
Class of Stock [Line Items]
Convertible preferred stock, authorized (in shares)		0		4,740,531
Convertible preferred stock, par value (in shares)		$ 0.0001		$ 0.0001
Convertible preferred stock, issued (in shares)		0		4,701,449
Convertible preferred stock, outstanding (in shares)		0		4,701,449
Series F
Class of Stock [Line Items]
Convertible preferred stock, authorized (in shares)		0		4,866,776
Convertible preferred stock, par value (in shares)		$ 0.0001		$ 0.0001
Convertible preferred stock, issued (in shares)		0		4,866,758
Convertible preferred stock, outstanding (in shares)		0		4,866,758
Series G
Class of Stock [Line Items]
Convertible preferred stock, authorized (in shares)		0		5,140,257
Convertible preferred stock, par value (in shares)		$ 0.0001		$ 0.0001
Convertible preferred stock, issued (in shares)		0		5,114,786
Convertible preferred stock, outstanding (in shares)		0		5,114,786
Series H
Class of Stock [Line Items]
Convertible preferred stock, authorized (in shares)		0		4,209,693
Convertible preferred stock, par value (in shares)		$ 0.0001		$ 0.0001
Convertible preferred stock, issued (in shares)		0		2,075,216
Convertible preferred stock, outstanding (in shares)		0		2,075,216
IPO
Class of Stock [Line Items]
Number of common stock shares converted	41,562,111
Number of shares issued for each share of convertible preferred stock converted (in shares)	1
Convertible preferred stock, authorized (in shares)	500,000
Convertible preferred stock, par value (in shares)	$ 0.0001