Comparative Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Jan. 03, 2020	Sep. 27, 2019	Jun. 28, 2019	Mar. 29, 2019	Dec. 28, 2018	Sep. 28, 2018	Jun. 29, 2018	Mar. 30, 2018	Jan. 03, 2020		Dec. 28, 2018		Dec. 29, 2017
Segment Reporting [Abstract]
Revenues before reimbursements	$ 102,220	$ 95,506	$ 100,263	$ 93,401	$ 85,269	$ 88,714	$ 89,972	$ 90,684	$ 391,390		$ 354,639		$ 329,664
Revenues	110,114	101,548	106,506	99,031	92,143	95,302	95,621	96,457	417,199	[1]	379,523	[1]	347,799	[1]
Operating Income	21,350	23,184	24,823	15,754	26,786	20,594	22,478	21,598	85,111		91,456		72,051
Income before income taxes	26,806	25,211	28,851	23,322	21,959	23,989	24,919	22,450
Net income (loss)	$ 19,121	$ 19,633	$ 20,994	$ 22,712	$ 16,036	$ 17,453	$ 18,425	$ 20,340	$ 82,460		$ 72,254		$ 41,305
Net income per share
Basic	$ 0.36	$ 0.37	$ 0.40	$ 0.43	$ 0.30	$ 0.33	$ 0.35	$ 0.39	$ 1.56		$ 1.37		$ 0.78
Diluted	$ 0.36	$ 0.36	$ 0.39	$ 0.42	$ 0.30	$ 0.32	$ 0.34	$ 0.38	$ 1.53		$ 1.33		$ 0.77
Shares used in per share computations
Shares used in basic per share computation	52,681	52,802	52,745	52,536	52,839	53,032	53,008	52,744	52,691		52,906		52,724
Diluted	53,817	54,002	53,872	53,814	54,119	54,302	54,195	54,012	53,884		54,168		53,972

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