Offering costs payable.

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Organization consolidation and presentation of financial statements line items.

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Working capital.

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Cash includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the customer may deposit additional funds at any time and effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid Investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Short-term investments, exclusive of cash equivalents, generally consist of marketable securities intended to be sold within one year (or the normal operating cycle if longer) and may include trading securities, available-for-sale securities, or held-to-maturity securities (if maturing within one year), as applicable.

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- Definition

Expense related to distribution, servicing and underwriting fees.

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Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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- Definition

The cash outflow for cost incurred directly with the issuance of an equity security.

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- Definition

The cash inflow associated with the amount received from entity's first offering of stock to the public.

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The cumulative amount of the reporting entity's undistributed earnings or deficit.

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- Definition

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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Number of new stock issued during the period.

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The Company and Basis of Presentation - Additional Information (Details)	1 Months Ended	6 Months Ended
	Apr. 30, 2018 USD ($) $ / shares shares	Jun. 30, 2018 USD ($) Segment	Dec. 31, 2017 USD ($)
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of operating segments \| Segment		1
Working capital		$ 72,700,000
Accumulated deficit		(90,046,000)	$ (72,513,000)
Cash, cash equivalents and marketable securities		72,200,000
Common Stock
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of shares issued \| shares	5,046,510
Public offering price \| $ / shares	$ 8.00
Proceeds from issuance of common stock upon initial public offering, net	$ 37,700,000
Underwriting discounts and commissions	2,400,000
Offering costs	$ 300,000
Common Stock \| Outstanding Liability
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Offering costs payable		$ 36,000
Common Stock \| Underwriters' Over-allotment Option
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of shares issued \| shares	546,510