Quarterly Financial Data (Unaudited) (Details) (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Jan. 03, 2015	Sep. 27, 2014	Jun. 28, 2014	Mar. 29, 2014	Dec. 28, 2013	Sep. 28, 2013	Jun. 29, 2013	Mar. 30, 2013	Jan. 03, 2015	Dec. 28, 2013	Dec. 29, 2012
Unaudited Interim Condensed Consolidated Financial Statements and Estimates
Revenues	$ 78,459,000	$ 73,483,000	$ 78,184,000	$ 76,245,000	$ 75,672,000	$ 74,427,000	$ 65,203,000	$ 63,130,000	$ 306,371,000	$ 278,432,000	$ 270,390,000
Gross profit	25,598,000	24,066,000	25,515,000	24,379,000	24,044,000	23,850,000	20,161,000	21,115,000	99,558,000	89,170,000	88,009,000
Income from operations	6,124,000	5,795,000	6,493,000	5,629,000	5,459,000	6,114,000	3,170,000	3,774,000	24,041,000	18,517,000	(57,810,000)
Income before provision for income taxes	6,022,000	5,575,000	6,334,000	5,384,000	5,221,000	5,952,000	3,368,000	3,377,000	23,315,000	17,918,000	(58,023,000)
Net income	3,743,000	3,189,000	3,167,000	3,308,000	3,716,000	3,333,000	1,351,000	2,835,000	13,407,000	11,235,000	(52,843,000)
Net (income) loss attributable to noncontrolling interest, net of tax	73,000	35,000	21,000	102,000	6,000	(63,000)	58,000	134,000	231,000	135,000	(147,000)
Net income attributable to CRA International, Inc.	3,816,000	3,224,000	3,188,000	3,410,000	3,722,000	3,270,000	1,409,000	2,969,000	13,638,000	11,370,000	(52,990,000)
Basic net income (loss) per share (in dollars per share)	$ 0.41	$ 0.33	$ 0.32	$ 0.34	$ 0.37	$ 0.32	$ 0.14	$ 0.30	$ 1.40	$ 1.13	$ (5.21)
Diluted net income (loss) per share (in dollars per share)	$ 0.40	$ 0.33	$ 0.32	$ 0.34	$ 0.37	$ 0.32	$ 0.14	$ 0.29	$ 1.38	$ 1.12	$ (5.21)
Deferred tax assets valuation error correction			$ 800,000
Weighted average number of shares outstanding:
Basic (in shares)	9,344	9,729	9,919	10,029	10,071	10,093	10,100	9,994	9,747	10,084	10,167
Diluted (in shares)	9,560	9,919	10,026	10,108	10,148	10,192	10,188	10,084	9,897	10,173	10,167