Number of common shares reserved for future issuance, as a percentage of shares outstanding.

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The number of shares authorized under the plan that were originally issued under a prior stock incentive plan.

+ References

No definition available.

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The fair value of nonvested awards on equity-based plans excluding option plans for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

+ References

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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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The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method.

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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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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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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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Number of additional shares authorized for issuance under an established share-based compensation plan.

+ References

No definition available.

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The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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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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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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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

Number of options outstanding, including both vested and non-vested options.

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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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Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands				3 Months Ended		12 Months Ended
	Jan. 01, 2019	Dec. 31, 2018	Jun. 27, 2018	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Options Outstanding		3,770,086		3,770,086		3,770,086	3,535,560
Aggregate intrinsic value of options exercised						$ 1,700	$ 1,400
Unvested Stock options		2,409,893		2,409,893		2,409,893	242,496
Stock-based compensation expense						$ 7,121	$ 1,860
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options expiration period						10 years
Employees And Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair value options granted price per share						$ 5.09	$ 3.28
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense related to unvested options		$ 32,500		$ 32,500		$ 32,500
Compensation expense, expected recognition period						5 years 6 months
Restricted Stock Units (RSUs) [Member] \| Performance Based And Service Based [Member] \| Non Probable Performance Based And Service Based [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested Stock options		129,750		129,750		129,750
Unvested grant-date fair value		$ 2,300
Share based compensation vesting period		3 years
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense related to unvested options		$ 7,700		$ 7,700		$ 7,700
Compensation expense, expected recognition period						3 years 2 months 12 days
Performance-Based (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense				$ 1,100	$ 600	$ 1,700
Class A Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Options Outstanding		1,383,428		1,383,428		1,383,428
Class A Common Stock or Class B Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Options Outstanding		2,386,658		2,386,658		2,386,658
2008 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation, common stock available for grant		8,440,712		8,440,712		8,440,712
Share-based Compensation, common stock available for grant			583,056
2018 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation, common stock available for grant		583,082		583,082		583,082
2018 Equity Incentive Plan [Member] \| Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation, number of additional shares available for issuance	1,261,257
2018 Equity Incentive Plan [Member] \| Class A Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation, common stock available for grant			2,149,480
2018 Equity Incentive Plan [Member] \| Class A Common Stock [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock available for issuance			2,500,000
2018 Equity Incentive Plan [Member] \| Class A Common Stock and Class B Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation, number of additional shares available from 2008 Stock Incentive Plan			583,056
2018 Equity Incentive Plan [Member] \| Class A Common Stock and Class B Common Stock [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation, common stock available for grant			5,028,832
Percentage of shares of common stock available for issuance			5.00%