Acquisitions - Summary of Unaudited Pro Forma Results of Operations (Detail) - Southern Counties and Fore Acquisition [Member] - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	9 Months Ended
Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
Business Acquisition [Line Items]
Operating revenues	$ 380,790	$ 335,369	$ 1,112,560	$ 964,705
Income (loss) from operations	23,633	(1,596)	69,799	15,915
Net income (loss)	$ 15,570	$ (2,903)	$ 44,332	$ 3,796
Earnings (loss) per common share:
Basic	$ 0.55	$ (0.10)	$ 1.56	$ 0.13
Diluted	$ 0.55	$ (0.10)	$ 1.56	$ 0.13

Business acquisition pro forma earnings per share.

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- Definition

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.

+ References

No definition available.

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- Definition

The pro forma basic net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(3)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

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-Publisher FASB
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The pro forma diluted net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

+ References

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- Definition

Amount after tax of pro forma income from continuing operations as if the business combination had been completed at the beginning of a period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
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- Definition

The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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The pro forma revenue for a period as if the business combination or combinations had been completed at the beginning of the period.

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