Fair Value of Financial Instruments - Summary of Reconciliation of Acquisition Related Contingent Consideration (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 28, 2015	Jun. 29, 2014	Jun. 28, 2015	Jun. 29, 2014
Fair Value Option Qualitative Disclosures Related To Election [Line Items]
Payments/accruals	$ (1,388)	$ 0	$ (2,105)	$ 0
Favorable fair value adjustment to contingent consideration liability	(6,078)	0	(989)	0
Ending balance	94,068	13,000	94,068	13,000
Johnson City And Morristown Territory Acquisition [Member]
Fair Value Option Qualitative Disclosures Related To Election [Line Items]
Increase due to an acquisition	0	13,000	0	13,000
Cleveland and Cookeville, Tennessee Territory Acquisitions [Member]
Fair Value Option Qualitative Disclosures Related To Election [Line Items]
Increase due to an acquisition	0	0	14,572	0
Louisville, Kentucky and Evansville, Indiana [Member]
Fair Value Option Qualitative Disclosures Related To Election [Line Items]
Increase due to an acquisition	0	0	32,711	0
Paducah And Pikeville Kentucky Territory Acquisitions [Member]
Fair Value Option Qualitative Disclosures Related To Election [Line Items]
Increase due to an acquisition	$ 3,029	$ 0	$ 3,029	$ 0