Quarterly Financial Data (Detail) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Jan. 01, 2016	Oct. 02, 2015	Jul. 03, 2015	Apr. 03, 2015	Jan. 02, 2015	Oct. 03, 2014	Jul. 04, 2014	Apr. 04, 2014	Jan. 01, 2016		Jan. 02, 2015		Jan. 03, 2014
Quarterly Financial Information [Line Items]
Revenues before reimbursements	$ 69,789	$ 74,503	$ 75,272	$ 76,141	$ 69,647	$ 74,264	$ 72,331	$ 72,967	$ 295,705		$ 289,209		$ 280,043
Revenues	73,681	78,994	79,864	80,293	73,611	78,557	76,574	75,962	312,832	[1]	304,704	[1]	296,168	[1]
Operating income	14,279	20,921	18,705	15,028	14,133	19,238	16,084	14,094	68,933		63,549		55,946
Income before income taxes	15,997	18,773	19,292	17,071	15,827	18,375	18,398	15,365	71,133		67,965		63,945
Net income	$ 9,850	$ 11,719	$ 11,697	$ 10,333	$ 9,243	$ 11,040	$ 11,264	$ 9,154	$ 43,599		$ 40,701		$ 38,640
Net income per share
Basic (in dollars per share)	$ 0.37	$ 0.44	$ 0.44	$ 0.39	$ 0.35	$ 0.41	$ 0.42	$ 0.34	$ 1.64		$ 1.51		$ 1.42
Diluted (in dollars per share)	$ 0.36	$ 0.43	$ 0.43	$ 0.38	$ 0.34	$ 0.40	$ 0.41	$ 0.33	$ 1.6		$ 1.47		$ 1.38
Shares used in per share computations
Basic	26,491	26,597	26,714	26,622	26,586	26,938	27,040	27,074	26,606		26,910		27,232
Diluted	27,133	27,268	27,368	27,390	27,318	27,648	27,746	27,880	27,298		27,666		28,050

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