Debt - Additional Information (Details) - USD ($)	1 Months Ended									3 Months Ended		9 Months Ended
	Oct. 31, 2019	May 31, 2019	Mar. 31, 2019	Aug. 31, 2018	Jul. 31, 2018	Apr. 30, 2018	Nov. 30, 2017	Oct. 31, 2017	Jan. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Debt Instrument [Line Items]
Net proceeds from sale of shares													$ 17,712,000
Silicon Valley Bank
Debt Instrument [Line Items]
Debt instrument, maturity date			Mar. 01, 2023			Jun. 01, 2020
Interest rate, terms												the Company is to make interest-only payments through December 31, 2019 with respect to Tranche 1 and Tranche 2 at a rate equal to the greater of the Prime Rate plus 1.00%, as defined in the 2019 Loan, or 6.5%, followed by an amortization period of 39 months of equal monthly payments of principal plus interest until paid in full.
Percentage of final payment on principal amount of refinanced advances			6.00%
Silicon Valley Bank | Tranche B
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity						$ 2,000,000
Line of credit facility, extended period						Apr. 30, 2018
Silicon Valley Bank | Tranche C
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity				$ 2,000,000
Interest only period extended					Aug. 31, 2018
Line of credit facility, extended period					Dec. 31, 2018	Jul. 31, 2018
Silicon Valley Bank | Prepayment Made Prior To First Anniversary | Loan and Security Agreement
Debt Instrument [Line Items]
Prepayment fee percentage								3.00%
Silicon Valley Bank | Prepayment Made By Second Anniversary | Loan and Security Agreement
Debt Instrument [Line Items]
Prepayment fee percentage								2.00%
Silicon Valley Bank | Prepayment Made After Second Anniversary | Loan and Security Agreement
Debt Instrument [Line Items]
Prepayment fee percentage								1.00%
Silicon Valley Bank | Tranche B and C
Debt Instrument [Line Items]
Interest only period extended						Dec. 31, 2018
Debt instrument, maturity date						Dec. 31, 2020
Silicon Valley Bank | Tranche 3
Debt Instrument [Line Items]
Amortization period of payments of principal plus interest amounts			33 months
Silicon Valley Bank | Tranche 1 and 2
Debt Instrument [Line Items]
Amortization period of payments of principal plus interest amounts			39 months
Interest rate			6.50%
Silicon Valley Bank | Tranche 1 and 2 | Prime Rate
Debt Instrument [Line Items]
Interest rate, percentage point added to reference rate			1.00%
SVB and WestRiver
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity			$ 15,000,000
Long-term Debt, Gross										$ 100,000		$ 100,000
SVB and WestRiver | Tranche 1
Debt Instrument [Line Items]
Number of warrants issued			37,606
Exercise price of warrant			$ 4.73
Line of credit facility, maximum borrowing capacity			$ 7,500,000
Proceeds from lines of credit			7,500,000
SVB and WestRiver | Tranche 2
Debt Instrument [Line Items]
Number of warrants issued		12,130
Exercise price of warrant		$ 10.86
Line of credit facility, maximum borrowing capacity		$ 2,500,000
Proceeds from lines of credit		$ 2,500,000
SVB and WestRiver | Tranche 3
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity			$ 5,000,000
SVB and WestRiver | Tranche 3 | Subsequent Event
Debt Instrument [Line Items]
Number of warrants issued	24,262
Exercise price of warrant	$ 3.88
Proceeds from lines of credit	$ 5,000,000
SVB and WestRiver | Tranche 1 and 2
Debt Instrument [Line Items]
Debt discount										300,000		300,000
SVB, SVB and WestRiver
Debt Instrument [Line Items]
Interest expense										300,000	$ 200,000	700,000	400,000
Term Loan | Silicon Valley Bank
Debt Instrument [Line Items]
Number of warrants issued								49,713
Exercise price of warrant								$ 9.659
Warrants exercisable date								Oct. 18, 2027
Line of credit facility, maximum borrowing capacity								$ 7,500,000
Interest only period extended								Dec. 31, 2018
Amortization period of payments of principal plus interest amounts								24 months
Percentage of aggregate principal amount								7.00%
Term Loan | Silicon Valley Bank | Tranche A
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity								$ 3,500,000
Proceeds from lines of credit							$ 3,500,000
Term Loan | Silicon Valley Bank | Tranche B
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity								2,000,000
Term Loan | Silicon Valley Bank | Tranche C
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity								$ 2,000,000
Series D Redeemable Preferred Stock
Debt Instrument [Line Items]
Sale of stock				1,842,959
Sale of stock price per share				$ 9.659
Net proceeds from sale of shares				$ 17,700,000
Debt converted into shares				2,080,209
Warrants | Series C-1
Debt Instrument [Line Items]
Number of warrants issued				368,582
Exercise price of warrant				$ 0.12
2017 Notes
Debt Instrument [Line Items]
Debt instrument principal amount									$ 14,700,000
Interest rate									8.00%
Proceeds from sale of equity									$ 10,000,000
Debt instrument, Redemption price, percentage									80.00%
Debt discount										3,000,000		3,000,000
Interest expense										0	$ 700,000	0	$ 3,400,000
2017 Notes | Warrants
Debt Instrument [Line Items]
Debt discount										$ 1,700,000		$ 1,700,000
Number of warrants issued										304,397		304,397
Exercise price of warrant										$ 0.12		$ 0.12
Warrants exercisable date												Jan. 31, 2024