Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 30, 2016	Sep. 30, 2016	Jul. 01, 2016	Apr. 01, 2016	Jan. 01, 2016	Oct. 02, 2015	Jul. 03, 2015	Apr. 03, 2015	Dec. 30, 2016		Jan. 01, 2016		Jan. 02, 2015
Quarterly Financial Information [Line Items]
Revenues before reimbursements	$ 72,753	$ 74,160	$ 73,334	$ 78,950	$ 69,789	$ 74,503	$ 75,272	$ 76,141	$ 299,197		$ 295,705		$ 289,209
Revenues	77,013	77,612	77,295	83,156	73,681	78,994	79,864	80,293	315,076	[1]	312,832	[1]	304,704	[1]
Operating income	14,949	15,595	14,931	16,436	14,279	20,921	18,705	15,028	61,911		68,933		63,549
Income before income taxes	16,791	17,920	16,677	17,734	15,997	18,773	19,292	17,071	69,122		71,133		67,965
Net income	$ 10,388	$ 11,289	$ 10,453	$ 15,350	$ 9,850	$ 11,719	$ 11,697	$ 10,333	$ 47,480		$ 43,599		$ 40,701
Net income per share
Basic (in dollars per share)	$ 0.40	$ 0.43	$ 0.39	$ 0.58	$ 0.37	$ 0.44	$ 0.44	$ 0.39	$ 1.79		$ 1.64		$ 1.51
Diluted (in dollars per share)	$ 0.39	$ 0.42	$ 0.38	$ 0.56	$ 0.36	$ 0.43	$ 0.43	$ 0.38	$ 1.75		$ 1.6		$ 1.47
Shares used in per share computations
Basic	26,262	26,545	26,631	26,513	26,491	26,597	26,714	26,622	26,488		26,606		26,910
Diluted	26,955	27,185	27,264	27,239	27,133	27,268	27,368	27,390	27,166		27,298		27,666

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