Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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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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The highest quantity of shares an employee can purchase under the plan per period.

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

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Purchase price of common stock expressed as a percentage of its fair value.

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

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The maximum amount of shares an employee can purchase under the plan per period.

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Represents the maximum percentage of cash compensation allowed to be deducted each pay period for the purchase of common stock by eligible employees.

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Stock-Based Compensation Plans - Additional Information (Details) - USD ($)		3 Months Ended
	May 24, 2007	Mar. 31, 2019	Mar. 31, 2018	Apr. 01, 2018
Employee Stock Purchase Plan
Stock-based compensation plans
Number of shares authorized				325,000
Maximum percentage of cash compensation allowed to be deducted for the purchase of common stock by eligible employees		10.00%
Maximum number of shares to be purchased by employee in one calendar year (in shares)		1,000
Maximum amount of shares to be purchased by employee in one calendar year (in dollars)		$ 25,000
Purchase price expressed as a percentage of the market price of the common stock on the purchase date or on the date of entry		85.00%
Shares issued (in shares)		6,732	5,497
2007 Stock Incentive Plan \| Restricted Stock
Stock-based compensation plans
Shares granted (in shares)		0
Number of shares authorized		2,800,000
Stock options outstanding (in shares)		0
Number of shares available for future issuance (in shares)		890,730
2007 Stock Incentive Plan \| Restricted Stock \| Minimum
Stock-based compensation plans
Vesting period	1 year
2007 Stock Incentive Plan \| Restricted Stock \| Maximum
Stock-based compensation plans
Vesting period	3 years
2018 Plan \| Restricted Stock
Stock-based compensation plans
Shares granted (in shares)		0
Number of shares authorized		800,000
2018 Plan \| Restricted Stock \| Minimum
Stock-based compensation plans
Vesting period		1 year
2018 Plan \| Restricted Stock \| Maximum
Stock-based compensation plans
Vesting period		3 years