Condensed Balance Sheets (Parenthetical) - $ / shares	Mar. 30, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Convertible preferred stock, par value (in shares)	$ 0.0001	$ 0.0001
Convertible preferred stock, authorized (in shares)	43,882,867	43,882,867
Convertible preferred stock, outstanding (in shares)	41,562,111	41,562,111	39,474,156	39,361,211
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, authorized (in shares)	60,000,000	58,669,600
Common stock, issued (in shares)	7,120,933	6,951,350
Common stock, outstanding (in shares)	7,120,933	6,951,350
Series A
Convertible preferred stock, par value (in shares)	$ 0.0001	$ 0.0001
Convertible preferred stock, authorized (in shares)	3,333,500	3,333,500
Convertible preferred stock, issued (in shares)	3,333,500	3,333,500
Convertible preferred stock, outstanding (in shares)	3,333,500	3,333,500
Series B
Convertible preferred stock, par value (in shares)	$ 0.0001	$ 0.0001
Convertible preferred stock, authorized (in shares)	4,802,260	4,802,260
Convertible preferred stock, issued (in shares)	4,680,565	4,680,565
Convertible preferred stock, outstanding (in shares)	4,680,565	4,680,565
Series C
Convertible preferred stock, par value (in shares)	$ 0.0001	$ 0.0001
Convertible preferred stock, authorized (in shares)	8,076,643	8,076,643
Convertible preferred stock, issued (in shares)	8,076,636	8,076,636
Convertible preferred stock, outstanding (in shares)	8,076,636	8,076,636
Series D
Convertible preferred stock, par value (in shares)	$ 0.0001	$ 0.0001
Convertible preferred stock, authorized (in shares)	8,713,207	8,713,207
Convertible preferred stock, issued (in shares)	8,713,201	8,713,201
Convertible preferred stock, outstanding (in shares)	8,713,201	8,713,201
Series E
Convertible preferred stock, par value (in shares)	$ 0.0001	$ 0.0001
Convertible preferred stock, authorized (in shares)	4,740,531	4,740,531
Convertible preferred stock, issued (in shares)	4,701,449	4,701,449
Convertible preferred stock, outstanding (in shares)	4,701,449	4,701,449
Series F
Convertible preferred stock, par value (in shares)	$ 0.0001	$ 0.0001
Convertible preferred stock, authorized (in shares)	4,866,776	4,866,776
Convertible preferred stock, issued (in shares)	4,866,758	4,866,758
Convertible preferred stock, outstanding (in shares)	4,866,758	4,866,758
Series G
Convertible preferred stock, par value (in shares)	$ 0.0001	$ 0.0001
Convertible preferred stock, authorized (in shares)	5,140,257	5,140,257
Convertible preferred stock, issued (in shares)	5,114,786	5,114,786
Convertible preferred stock, outstanding (in shares)	5,114,786	5,114,786
Series H
Convertible preferred stock, par value (in shares)	$ 0.0001	$ 0.0001
Convertible preferred stock, authorized (in shares)	4,209,693	4,209,693
Convertible preferred stock, issued (in shares)	2,075,216	2,075,216
Convertible preferred stock, outstanding (in shares)	2,075,216	2,075,216

Face amount or stated value per share of common stock.

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