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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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		3 Months Ended
	May 24, 2007	Mar. 31, 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		337,784
Employee Stock Purchase Plan
Stock-based compensation plans
Number of shares authorized			250,000
Restricted stock \| The 2007 plan
Stock-based compensation plans
Number of shares awarded		2,628,960
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
Maximum \| Restricted stock \| The 2007 plan
Stock-based compensation plans
Vesting period	4 years