Net Income per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 04, 2015	Jun. 28, 2014	Jul. 04, 2015	Jun. 28, 2014
Net Income (Loss) Available to Common Stockholders, Diluted [Abstract]
Net income attributable to CRA International, Inc. allocated to common shares	$ 3,325	$ 3,188	$ 6,104	$ 6,598
Less: net income attributable to CRA International, Inc. allocated to unvested shares			(47)
Net income attributable to CRA International, Inc. allocated to common shares			$ 6,057
Weighted Average Number of Shares Outstanding, Diluted [Abstract]
Net income attributable to CRA International, Inc. allocated to common shares (in shares)			9,183,000
Less: net income attributable to CRA International, Inc. allocated to unvested shares (in shares)			(71,000)
Net income attributable to CRA International, Inc. allocated to common shares (in shares)	9,034,000	9,919,000	9,112,000	9,974,000
Income (Loss) from Operations before Extraordinary Items, Per Basic Share [Abstract]
Net income attributable to CRA International, Inc. allotted to common shares (in dollars per share)	$ 0.37	$ 0.32	$ 0.66	$ 0.66
Reconciliation of basic to diluted weighted average shares of common stock outstanding
Basic weighted average shares outstanding	9,034,000	9,919,000	9,112,000	9,974,000
Common stock equivalents:
Stock options, restricted shares, and restricted stock units (in shares)	219,000	107,000	216,000	93,000
Diluted weighted average shares outstanding	9,253,000	10,026,000	9,328,000	10,067,000
Calculation of common stock equivalents for purposes of computing diluted weighted average shares outstanding
Anti-dilutive securities excluded from EPS computation (in shares)	371,421	888,746	381,577	1,088,180