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

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Stock-Based Compensation Plans - 2007 Stock Incentive Plan (Details) - shares		9 Months Ended
	May 24, 2007	Sep. 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		169,144
Number of shares available		885,730
Employee Stock Purchase Plan
Stock-based compensation plans
Number of shares authorized			325,000
Restricted Stock \| The 2007 plan
Stock-based compensation plans
Stock options outstanding (in shares)		0
Number of shares awarded		2,883,414
Restricted Stock \| 2018 Plan
Stock-based compensation plans
Number of shares authorized		800,000
Minimum \| Restricted Stock \| The 2007 plan
Stock-based compensation plans
Vesting period	1 year
Minimum \| Restricted Stock \| 2018 Plan
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 Plan
Stock-based compensation plans
Vesting period		4 years