Earnings Per Share Note [Line Items]

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- Definition

Number of Employees

+ References

No definition available.

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- Definition

Employee tenure requirement to participate in plan.

+ References

No definition available.

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- Definition

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

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- Definition

Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

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.

+ References

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

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

+ References

No definition available.

+ Details

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- Definition

The addition or reduction in the number of reserved shares that could potentially be issued under the option plan attributable to reasons other than grants, exercises, forfeitures, and expirations during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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Net Income per Share - Additional Information (Detail)				3 Months Ended		9 Months Ended		12 Months Ended
Net Income per Share - Additional Information (Detail)	Aug. 01, 2017	Mar. 03, 2017	Jan. 01, 2017	Sep. 30, 2017 shares	Sep. 24, 2016 shares	Sep. 30, 2017 shares	Sep. 24, 2016 shares	Dec. 31, 2016 Employee shares
Earnings Per Share Note [Line Items]
Stock options cancelled during the period						12,208
Investment Share Program
Earnings Per Share Note [Line Items]
Requirement tenure of employee for investment share program, purchase shares at discount						2 years
Vesting period			5 years
Investment Share Program \| Minimum
Earnings Per Share Note [Line Items]
Requirement tenure of employee for investment share program						1 year
Discount from current market value						20.00%
Investment Share Program \| Maximum
Earnings Per Share Note [Line Items]
Discount from current market value						40.00%
Restricted Stock Awards
Earnings Per Share Note [Line Items]
Vesting period			5 years
Restricted Stock Awards \| Key Employee
Earnings Per Share Note [Line Items]
Vesting period	5 years	5 years
Common Class A
Earnings Per Share Note [Line Items]
Antidilutive securities excluded from computation of earnings per share				791,000	740,000	800,000	704,000
Common Class A \| Performance-Based Awards
Earnings Per Share Note [Line Items]
Number of shares not included because the performance criteria was not met as of the end of the reporting period						36,000	35,000
Stock options cancelled during the period						12,000
Common Class A \| Performance-Based Awards \| Key Employee
Earnings Per Share Note [Line Items]
Options granted in period								31,000
Number of employees \| Employee								2
Common Class A \| Performance-Based Awards \| Executive Officers
Earnings Per Share Note [Line Items]
Options granted in period						5,000