Summary of Significant Accounting Policies - Narrative (Details) - USD ($)	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Accounting Policies [Abstract]
Restricted cash	$ 422,000		$ 316,000
Allowance for doubtful accounts	0		0
Payment of offering costs related to initial public offering	221,000	$ 0
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue	4,000,000		3,100,000
Deferred offering costs	4,257,000		0
Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue	$ 1,000,000		$ 1,500,000

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For an unclassified balance sheet, a valuation allowance for receivables due a company that are expected to be uncollectible.

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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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Specific incremental costs directly attributable to a proposed or actual offering of securities which are deferred at the end of the reporting period.

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Amount of deferred revenue as of balance sheet date. Deferred revenue represents collections of cash or other assets related to a revenue producing activity for which revenue has not yet been recognized. Generally, an entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP.

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

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Amount of cash and cash equivalents restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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