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 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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Number of shares (or other type of equity) issued during the period as a result of any equity-based compensation plan other than an employee stock ownership plan (ESOP), net of any shares forfeited. Shares issued could result from the issuance of restricted stock, the exercise of stock options, stock issued under employee stock purchase plans, and/or other employee benefit plans.

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Represents the aggregate amount of shares that have been forfeited and returned to the pool of shares which could be granted under the plan.

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Stock-Based Compensation Plans - 2007 Stock Incentive Plan (Details) - shares		6 Months Ended
	May 24, 2007	Jun. 30, 2018	May 10, 2010
The 2007 plan
Stock-based compensation plans
Number of shares authorized	2,800,000
Restricted stock, forfeited, and returned to pool		166,744
Number of shares available		83,330
Employee Stock Purchase Plan
Stock-based compensation plans
Number of shares authorized			325,000
Restricted stock \| The 2007 plan
Stock-based compensation plans
Number of shares awarded		2,883,414
Restricted stock \| 2018 Stock Incentive Plan [Member]
Stock-based compensation plans
Number of shares authorized		800,000
Stock Option \| The 2007 plan
Stock-based compensation plans
Stock options outstanding (in shares)		0
Minimum \| Restricted stock \| The 2007 plan
Stock-based compensation plans
Vesting period	1 year
Minimum \| Restricted stock \| 2018 Stock Incentive Plan [Member]
Stock-based compensation plans
Vesting period		1 year
Maximum \| Restricted stock \| The 2007 plan
Stock-based compensation plans
Vesting period	4 years
Maximum \| Restricted stock \| 2018 Stock Incentive Plan [Member]
Stock-based compensation plans
Vesting period		4 years