Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Aggregate number of common shares reserved for future issuance.

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- Definition

Unrecognized cost of unvested share-based compensation awards.

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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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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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- Definition

Discount rate from fair value on purchase date that participants pay for shares.

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- Definition

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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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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- Definition

Net number of share options (or share units) granted during the period.

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- Definition

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

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Equity Incentive Plans - Narrative (Details) - USD ($) $ in Millions		3 Months Ended
	Apr. 24, 2018	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted (in shares)		0
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation expense		$ 5.6	$ 4.3
Unrecognized compensation costs related to non vested stock option awards		$ 28.9
Expected weighted average period to recognize expense		2 years 10 months 8 days
Granted shares (in shares)		0
Restricted Stock \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		3 years
Restricted Stock \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		4 years
Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Discount on purchase of Common Stock for employee from the current market price		5.00%
Maximum shares authorized under ESPP for sale offer to eligible employees (in shares)		750,000
Shares issued (in shares)		6,867
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation expense		$ 0.2	$ 0.7
Unrecognized compensation costs related to non vested stock option awards		$ 1.7
Expected weighted average period to recognize expense		2 years 8 months 2 days
Subsequent Event \| Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted shares (in shares)	914,000
Subsequent Event \| 2018 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for issuance	4,600,000