Operations in Different Geographic Areas (Detail) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 28, 2018	Sep. 28, 2018	Jun. 29, 2018	Mar. 30, 2018	Dec. 29, 2017	Sep. 29, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 28, 2018		Dec. 29, 2017		Dec. 30, 2016
Operations in Different Geographic Areas [Line Items]
Property, Equipment and Leasehold Improvements, net		$ 46,103				$ 35,014				$ 46,103		$ 35,014
Revenues		92,143	$ 95,302	$ 95,621	$ 96,457	88,282	$ 87,555	$ 87,840	$ 84,122	379,523	[1]	347,799	[1]	$ 315,076	[1]
United States
Operations in Different Geographic Areas [Line Items]
Property, Equipment and Leasehold Improvements, net		44,181				33,771				44,181		33,771
Revenues	[1]									334,422		308,406		281,223
Foreign Countries
Operations in Different Geographic Areas [Line Items]
Property, Equipment and Leasehold Improvements, net		$ 1,922				$ 1,243				1,922		1,243
Revenues	[1]									$ 45,101		$ 39,393		$ 33,853

[1] Geographic revenues are allocated based on the location of the client.