Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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- Definition

Aggregate number of common shares reserved for future issuance.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Unrecognized cost of unvested options awarded to employees as compensation.

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Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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- Definition

Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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- Definition

Number of shares issued during the period as a result of an employee stock purchase plan.

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Stock-Based Compensation - Additional Information (Detail) - USD ($)		1 Months Ended	3 Months Ended	9 Months Ended
	Apr. 25, 2017	May 31, 2017	Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service period for option exercise				5 years
Stock-based compensation expense			$ 1,574,000	$ 10,919,000
Granted				$ 5.04	$ 4.38
Vested				$ 5,300,000	$ 0
Compensation cost related to nonvested stock options not yet recognized			12,600,000	$ 12,600,000
Unrecognized compensation cost related to nonvested stock option recognized over weighted average period, in years				3 years
Aggregate purchase of stock options	216,160
Cumulative Stock-based Compensation Expense Related to Stock Options Recorded upon Effectiveness of Our IPO
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense			0	$ 6,236,000
Cumulative Stock-based Compensation Expense Related to Stock Options Recorded upon Effectiveness of Our IPO \| Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 6,200,000
Stock Option Modifications
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 2,400,000		$ 0	$ 2,394,000
2017 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available to be issued			6,425,767	6,425,767
2017 Equity Incentive Plan \| Class A Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available to be issued		6,421,442	6,481,622	6,481,622
2007 Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available to be issued		421,442
Number of shares available for grants		0
Period for which options can be granted				10 years