Quarterly Financial Data (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Jan. 02, 2015	Oct. 03, 2014	Jul. 04, 2014	Apr. 04, 2014	Jan. 03, 2014	Sep. 27, 2013	Jun. 28, 2013	Mar. 29, 2013	Jan. 02, 2015		Jan. 03, 2014		Dec. 28, 2012
Quarterly Financial Information [Line Items]
Revenues before reimbursements	$ 69,647	$ 74,264	$ 72,331	$ 72,967	$ 69,036	$ 70,096	$ 71,919	$ 68,992	$ 289,209		$ 280,043		$ 266,562
Revenues	73,611	78,557	76,574	75,962	72,772	75,231	75,505	72,660	304,704	[1]	296,168	[1]	292,653	[1]
Operating income	14,133	19,238	16,084	14,094	12,342	15,160	17,593	10,851	63,549		55,946		57,620
Income before income taxes	15,827	18,375	18,398	15,365	14,654	17,515	18,271	13,505	67,965		63,945		61,749
Net income	$ 9,243	$ 11,040	$ 11,264	$ 9,154	$ 8,722	$ 11,094	$ 10,848	$ 7,976	$ 40,701		$ 38,640		$ 37,225
Net income per share
Basic (in dollars per share)	$ 0.70	$ 0.82	$ 0.83	$ 0.68	$ 0.64	$ 0.82	$ 0.80	$ 0.58	$ 3.02		$ 2.84		$ 2.70
Diluted (in dollars per share)	$ 0.68	$ 0.80	$ 0.81	$ 0.66	$ 0.63	$ 0.79	$ 0.77	$ 0.56	$ 2.94		$ 2.76		$ 2.60
Shares used in per share computations
Basic	13,293	13,469	13,520	13,537	13,556	13,598	13,637	13,667	13,455		13,616		13,780
Diluted	13,659	13,824	13,873	13,940	13,949	13,993	14,007	14,125	13,833		14,025		14,293

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