Debt - Additional Information (Details)	1 Months Ended							3 Months Ended
	Mar. 31, 2019 USD ($) d $ / shares shares	Aug. 31, 2018 USD ($) $ / shares shares	Jul. 31, 2018 USD ($)	Apr. 30, 2018 USD ($)	Nov. 30, 2017 USD ($)	Oct. 31, 2017 USD ($) $ / shares shares	Jan. 31, 2017 USD ($)	Mar. 31, 2019 USD ($) $ / shares shares	Mar. 31, 2018 USD ($)	May 31, 2019 USD ($)
Silicon Valley Bank
Debt Instrument [Line Items]
Interest expense								$ 200,000	$ 100,000
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 on 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%							6.00%
Long-term Debt, Gross	$ 4,000							$ 4,000
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 1
Debt Instrument [Line Items]
Debt discount	200,000							200,000
Proceeds from lines of credit	$ 7,500,000
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							$ 15,000,000
Threshold trading days | d	10
SVB and WestRiver | Tranche 1
Debt Instrument [Line Items]
Number of warrants issued | shares	37,606							37,606
Exercise price of warrant | $ / shares	$ 4.73							$ 4.73
Line of credit facility, maximum borrowing capacity	$ 7,500,000							$ 7,500,000
SVB and WestRiver | Tranche 2
Debt Instrument [Line Items]
Number of warrants issued | shares	12,131							12,131
SVB and WestRiver | Tranche 2 | Scenario, Forecast
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity										$ 2,500,000
SVB and WestRiver | Tranche 3
Debt Instrument [Line Items]
Number of warrants issued | shares	24,262							24,262
Line of credit facility, maximum borrowing capacity	$ 5,000,000							$ 5,000,000
Term Loan | Silicon Valley Bank
Debt Instrument [Line Items]
Number of warrants issued | shares						49,713
Exercise price of warrant | $ / shares						$ 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 | shares		1,842,959
Sale of stock price per share | $ / shares		$ 9.659
Net proceeds from sale of shares		$ 17,700,000
Debt converted into shares | shares		2,080,209
Warrants | Series C-1
Debt Instrument [Line Items]
Number of warrants issued | shares		368,582
Exercise price of warrant | $ / shares		$ 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	$ 1,300,000
2017 Notes | Warrants
Debt Instrument [Line Items]
Debt discount	$ 1,700,000							$ 1,700,000
Number of warrants issued | shares	304,397							304,397
Exercise price of warrant | $ / shares	$ 0.12							$ 0.12
Warrants exercisable date								Jan. 31, 2024