Quarterly Financial Data (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Jan. 03, 2014	Sep. 27, 2013	Jun. 28, 2013	Mar. 29, 2013	Dec. 28, 2012	Sep. 28, 2012	Jun. 29, 2012	Mar. 30, 2012	Jan. 03, 2014		Dec. 28, 2012		Dec. 30, 2011
Quarterly Financial Information [Line Items]
Revenues before reimbursements	$ 69,036	$ 70,096	$ 71,919	$ 68,992	$ 65,049	$ 66,725	$ 68,318	$ 66,470	$ 280,043		$ 266,562		$ 246,667
Revenues	72,772	75,231	75,505	72,660	72,946	73,298	74,484	71,925	296,168	[1]	292,653	[1]	272,446	[1]
Operating income	12,342	15,160	17,593	10,851	13,715	14,728	17,361	11,816	55,946		57,620		53,460
Income before income taxes	14,654	17,515	18,271	13,505	14,438	16,330	17,248	13,733	63,945		61,749		54,819
Net income	$ 8,722	$ 11,094	$ 10,848	$ 7,976	$ 8,472	$ 10,225	$ 10,327	$ 8,201	$ 38,640		$ 37,225		$ 32,695
Net income per share
Basic (in dollars per share)	$ 0.64	$ 0.82	$ 0.80	$ 0.58	$ 0.62	$ 0.75	$ 0.75	$ 0.59	$ 2.84		$ 2.70		$ 2.31
Diluted (in dollars per share)	$ 0.63	$ 0.79	$ 0.77	$ 0.56	$ 0.60	$ 0.72	$ 0.72	$ 0.57	$ 2.76		$ 2.60		$ 2.22
Shares used in per share computations
Basic	13,556	13,598	13,637	13,667	13,733	13,694	13,835	13,859	13,616		13,780		14,181
Diluted	13,949	13,993	14,007	14,125	14,208	14,196	14,316	14,419	14,025		14,293		14,751

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