Summary of Gross revenues and reimbursements (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 28, 2012	Sep. 28, 2012	Jun. 29, 2012	Mar. 30, 2012	Dec. 30, 2011	Sep. 30, 2011	Jul. 01, 2011	Apr. 01, 2011	Dec. 28, 2012	Dec. 30, 2011	Dec. 31, 2010
Gross Revenues and Reimbursements [Line Items]
Gross revenues									$ 298,818	$ 280,671	$ 260,413
Less: Subcontractor fees									6,165	8,225	11,660
Revenues	72,946	73,298	74,484	71,925	67,916	65,951	65,106	73,473	292,653	272,446	248,753
Reimbursements:
Out-of-pocket reimbursements									6,426	6,162	4,870
Other outside direct expenses									19,665	19,617	22,023
Reimbursements									26,091	25,779	26,893
Revenues before reimbursements	$ 65,049	$ 66,725	$ 68,318	$ 66,470	$ 60,524	$ 61,387	$ 60,573	$ 64,183	$ 266,562	$ 246,667	$ 221,860