Date when an entity was incorporated

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- Definition

Number of classes of authorized common stock.

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- Definition

Number of votes per share.

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Conversion ratio of preferred stock to common stock.

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No definition available.

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Conversion ratio of preferred stock warrants to common stock warrants.

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No definition available.

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The number of shares converted in a noncash (or part noncash) transaction. Noncash is defined as transactions during a period that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

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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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No definition available.

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Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

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Cash paid for expenses incurred during underwriting activities (the process to review insurance applications, evaluate risks, accept or reject applications, and determine the premiums to be charged) for insurance companies.

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

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

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Date the subsidiary or equity investee issued or sold stock, in CCYY-MM-DD format.

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Price of a single share of a number of saleable stocks of a company.

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Number of new stock issued during the period.

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The Company - Additional Information (Details) $ / shares in Units, shares in Millions, $ in Millions		12 Months Ended
	Oct. 02, 2017 USD ($) ClassesofStock Vote $ / shares shares	Dec. 31, 2018 USD ($) segment	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Entity Wide Revenue Major Customer [Line Items]
Conversion date		Feb. 01, 2008
Number of reportable segments operates \| segment		2
Number of classes of authorized common stock \| ClassesofStock	2
Class A Common Stock
Entity Wide Revenue Major Customer [Line Items]
Number of votes per share \| Vote	1
Class B Common Stock
Entity Wide Revenue Major Customer [Line Items]
Number of votes per share \| Vote	10
Initial Public Offering \| Class B Common Stock Warrants
Entity Wide Revenue Major Customer [Line Items]
Warrants conversion ratio	100.00%
Initial Public Offering \| Class A Common Stock
Entity Wide Revenue Major Customer [Line Items]
Initial public offering completed date	Oct. 02, 2017
Number of shares sold \| shares	10.4
Share sold price per share \| $ / shares	$ 14.00
Net proceeds from shares sold \| $	$ 134.8
Underwriting discounts and commissions \| $	10.1
Offering costs incurred \| $	$ 3.1	$ 3.1	$ 3.1	$ 3.1
Initial Public Offering \| Class B Common Stock
Entity Wide Revenue Major Customer [Line Items]
Convertible preferred stock, Shares converted \| shares	80.8
Stock conversion ratio	100.00%
Over-Allotment Option \| Class A Common Stock
Entity Wide Revenue Major Customer [Line Items]
Number of shares sold \| shares	1.4