Goodwill - Schedule of Reconciliation of Activity for Goodwill (Detail) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019	Apr. 01, 2018
Goodwill And Intangible Assets Disclosure [Abstract]
Beginning balance - goodwill		$ 165,903	$ 169,316
Goodwill, Measurement period adjustments	[1]	0	946
Ending balance - goodwill		$ 165,903	$ 170,262

[1] Measurement period adjustments relate to post-closing adjustments made in accordance with the terms and conditions of the applicable asset purchase agreement or asset exchange agreement for distribution territories acquired or exchanged 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.