Amortization period of payments of principal plus interest amounts.

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Debt instrument prepayment fee percentage.

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Interest only period extended.

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Line of credit facility extended period.

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Date the warrants or rights are exercisable, in CCYY-MM-DD format.

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Exercise price per share or per unit of warrants or rights outstanding.

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Number of securities into which the class of warrant or right may be converted. For example, but not limited to, 500,000 warrants may be converted into 1,000,000 shares.

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The number of shares issued in exchange for the original debt being converted in a noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or payments in the period.

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Face (par) amount of debt instrument at time of issuance.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

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Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

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Percentage of principal amount of debt redeemed.

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Amount, after accumulated amortization, of debt discount.

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Amount of the cost of borrowed funds accounted for as interest expense for debt.

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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The cash inflow from issuance of callable preferred stock which is identified as being convertible to another type of financial security at the option of the issuer or the holder.

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The cash inflow from the issuance of common stock, preferred stock, treasury stock, stock options, and other types of equity.

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Amount of cash inflow from contractual arrangement with the lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

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Per share amount received by subsidiary or equity investee for each share of common stock issued or sold in the stock transaction.

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The number of securities classified as temporary equity that have been sold (or granted) to the entity's shareholders. Securities issued include securities outstanding and securities held in treasury. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with put option held by ESOP and stock redeemable by holder only in the event of a change in control of the issuer.

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Debt - Additional Information (Details) - USD ($)	1 Months Ended						3 Months Ended		9 Months Ended
Debt - Additional Information (Details) - USD ($)	Aug. 31, 2018	Jul. 31, 2018	Apr. 30, 2018	Nov. 30, 2017	Oct. 31, 2017	Jan. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Debt Instrument [Line Items]
Sale of stock							13,200,115		13,200,115		9,131,999
Net proceeds from the sale of redeemable convertible preferred stock									$ 17,712,000
Long-term debt, net of discount							$ 7,500,000		7,500,000
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
Interest expense							200,000		400,000
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%
Debt instrument, maturity date			Jun. 01, 2020
Long-term Debt, gross							7,500,000		7,500,000		$ 3,500,000
Long-term debt, net of discount							7,500,000		7,500,000		$ 3,400,000
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		2,000,000
Line of credit facility, extended period			Apr. 30, 2018
Term Loan \| Silicon Valley Bank \| Tranche C
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 2,000,000			$ 2,000,000
Interest only period extended		Aug. 31, 2018
Line of credit facility, extended period		Dec. 31, 2018	Jul. 31, 2018
Term Loan \| Silicon Valley Bank \| Prepayment Made Prior To First Anniversary \| Loan and Security Agreement
Debt Instrument [Line Items]
Prepayment fee percentage					3.00%
Term Loan \| Silicon Valley Bank \| Prepayment Made By Second Anniversary \| Loan and Security Agreement
Debt Instrument [Line Items]
Prepayment fee percentage					2.00%
Term Loan \| Silicon Valley Bank \| Prepayment Made After Second Anniversary \| Loan and Security Agreement
Debt Instrument [Line Items]
Prepayment fee percentage					1.00%
Term Loan \| Silicon Valley Bank \| Tranche B and C
Debt Instrument [Line Items]
Debt discount							$ 400,000		$ 400,000
Interest only period extended			Dec. 31, 2018
Debt instrument, maturity date			Dec. 31, 2020
Series D
Debt Instrument [Line Items]
Sale of stock	1,842,959						3,923,168		3,923,168
Sale of stock price per share	$ 9.659
Net proceeds from the sale of redeemable convertible preferred stock	$ 17,700,000
Debt converted into shares	2,080,209
Series C-1
Debt Instrument [Line Items]
Sale of stock							2,319,228		2,319,228		2,174,280
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							700,000	$ 600,000	3,400,000	$ 1,600,000
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