Fair Values of Financial Instruments - Summary of Reconciliation of Acquisition Related Contingent Consideration (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jul. 01, 2018	Jun. 30, 2019	Jul. 01, 2018
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Payments of acquisition related contingent consideration				$ 12,836	$ 11,263
Increase in fair value				43,268	3,957
Level 3 [Member]
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning balance - Level 3 liability		$ 393,007	$ 368,804	382,898	381,291
Measurement period adjustment	[1]		3,151		2,092
Payments of acquisition related contingent consideration		(6,599)	(5,381)	(12,836)	(11,263)
Reclassification to current payables		(3,180)	(1,180)	(880)	(1,540)
Increase in fair value		29,222	9,143	43,268	3,957
Ending balance - Level 3 liability		$ 412,450	$ 374,537	$ 412,450	$ 374,537

[1] Measurement period adjustments relate to post-closing adjustments made in accordance with the terms and conditions of the applicable asset purchase agreement for distribution territories acquired by the Company in April 2017 and October 2017 as part of the System Transformation. All final post-closing adjustments for these transactions were completed during 2018.