CONDENSED CONSOLIDATED STATEMENT OF SHAREHOLDERS' EQUITY (unaudited) - USD ($) $ in Thousands	CRA International, Inc. Shareholders' Equity	Common Stock	Retained Earnings	Accumulated Other Comprehensive Loss	Noncontrolling Interest	Total
Increase (Decrease) in Shareholders' Equity
Cumulative effect of a change in accounting principle related to ASC 606	$ 366		$ 366			$ 366
Balance, as adjusted	207,274	$ 47,414	169,756	$ (9,896)	$ 321	207,595
BALANCE at Dec. 30, 2017	206,908	$ 47,414	169,390	(9,896)	321	207,229
BALANCE (in shares) at Dec. 30, 2017		8,297,172
Increase (Decrease) in Shareholders' Equity
Net income	4,886		4,886			4,886
Foreign currency translation adjustment	1,318			1,318		1,318
Exercise of stock options	535	$ 535				535
Exercise of stock options (in shares)		24,688
Share-based compensation expense	1,292	$ 1,292				1,292
Restricted shares vestings (in shares)		97,722
Redemption of vested employee restricted shares for tax withholding	(1,783)	$ (1,783)				(1,783)
Redemption of vested employee restricted shares for tax withholding (in shares)		(35,287)
Shares repurchased	(8,057)	$ (8,057)				(8,057)
Shares repurchased (in shares)		(162,892)
Accrued dividends on unvested shares	10		10			10
Cash paid on dividend equivalents	(98)		(98)			(98)
Cash dividends paid to shareholders (per share)	(1,423)		(1,423)			(1,423)
BALANCE at Mar. 31, 2018	203,954	$ 39,401	173,131	(8,578)	321	204,275
BALANCE (in shares) at Mar. 31, 2018		8,221,403
BALANCE at Dec. 30, 2017	206,908	$ 47,414	169,390	(9,896)	321	207,229
BALANCE (in shares) at Dec. 30, 2017		8,297,172
Increase (Decrease) in Shareholders' Equity
Net income						15,633
Foreign currency translation adjustment						(1,483)
BALANCE at Sep. 29, 2018	200,263	$ 30,601	181,041	(11,379)	280	200,543
BALANCE (in shares) at Sep. 29, 2018		8,064,510
BALANCE at Mar. 31, 2018	203,954	$ 39,401	173,131	(8,578)	321	204,275
BALANCE (in shares) at Mar. 31, 2018		8,221,403
Increase (Decrease) in Shareholders' Equity
Net income	6,839		6,839			6,839
Foreign currency translation adjustment	(2,603)			(2,603)		(2,603)
Exercise of stock options	381	$ 381				381
Exercise of stock options (in shares)		19,395
Share-based compensation expense	1,146	$ 1,146				1,146
Restricted shares vestings (in shares)		513
Shares repurchased	(12,064)	$ (12,064)				(12,064)
Shares repurchased (in shares)		(215,585)
Accrued dividends on unvested shares	(44)		(44)			(44)
Cash dividends paid to shareholders (per share)	(1,372)		(1,372)			(1,372)
BALANCE at Jun. 30, 2018	196,237	$ 28,864	178,554	(11,181)	321	196,558
BALANCE (in shares) at Jun. 30, 2018		8,025,726
Increase (Decrease) in Shareholders' Equity
Net income	3,908		3,908			3,908
Foreign currency translation adjustment	(198)			(198)		(198)
Exercise of stock options	471	$ 471				471
Exercise of stock options (in shares)		21,374
Share-based compensation expense	1,266	$ 1,266				1,266
Restricted shares vestings (in shares)		17,410
Distribution to noncontrolling interest					(41)	(41)
Accrued dividends on unvested shares	(48)		(48)			(48)
Cash dividends paid to shareholders (per share)	(1,373)		(1,373)			(1,373)
BALANCE at Sep. 29, 2018	$ 200,263	$ 30,601	181,041	(11,379)	$ 280	200,543
BALANCE (in shares) at Sep. 29, 2018		8,064,510
BALANCE at Dec. 29, 2018		$ 22,837	186,229	(12,594)		$ 196,472
BALANCE (in shares) at Dec. 29, 2018		8,010,480				8,010,480
Increase (Decrease) in Shareholders' Equity
Net income			4,665			$ 4,665
Foreign currency translation adjustment				712		712
Exercise of stock options		$ 1,526				1,526
Exercise of stock options (in shares)		64,700
Share-based compensation expense		$ 911				911
Restricted shares vestings (in shares)		25,484
Redemption of vested employee restricted shares for tax withholding		$ (388)				(388)
Redemption of vested employee restricted shares for tax withholding (in shares)		(8,157)
Shares repurchased		$ (4,349)				(4,349)
Shares repurchased (in shares)		(86,609)
Accrued dividends on unvested shares			(8)			(8)
Cash paid on dividend equivalents			(35)			(35)
Cash dividends paid to shareholders (per share)			(1,616)			(1,616)
BALANCE at Mar. 30, 2019		$ 20,537	189,235	(11,882)		197,890
BALANCE (in shares) at Mar. 30, 2019		8,005,898
BALANCE at Dec. 29, 2018		$ 22,837	186,229	(12,594)		$ 196,472
BALANCE (in shares) at Dec. 29, 2018		8,010,480				8,010,480
Increase (Decrease) in Shareholders' Equity
Net income						$ 15,984
Foreign currency translation adjustment						(1,429)
BALANCE at Sep. 28, 2019		$ 9,028	197,347	(14,023)		$ 192,352
BALANCE (in shares) at Sep. 28, 2019		7,707,886				7,707,886
BALANCE at Mar. 30, 2019		$ 20,537	189,235	(11,882)		$ 197,890
BALANCE (in shares) at Mar. 30, 2019		8,005,898
Increase (Decrease) in Shareholders' Equity
Net income			5,580			5,580
Foreign currency translation adjustment				(653)		(653)
Share-based compensation expense		$ 848				848
Restricted shares vestings (in shares)		513
Shares repurchased		$ (7,161)				(7,161)
Shares repurchased (in shares)		(177,101)
Accrued dividends on unvested shares			(44)			(44)
Cash dividends paid to shareholders (per share)			(1,580)			(1,580)
BALANCE at Jun. 29, 2019		$ 14,224	193,191	(12,535)		194,880
BALANCE (in shares) at Jun. 29, 2019		7,829,310
Increase (Decrease) in Shareholders' Equity
Net income			5,739			5,739
Foreign currency translation adjustment				(1,488)		(1,488)
Exercise of stock options		$ 480				480
Exercise of stock options (in shares)		21,224
Share-based compensation expense		$ 882				882
Restricted shares vestings (in shares)		14,754
Shares repurchased		$ (6,558)				(6,558)
Shares repurchased (in shares)		(157,402)
Accrued dividends on unvested shares			(37)			(37)
Cash dividends paid to shareholders (per share)			(1,546)			(1,546)
BALANCE at Sep. 28, 2019		$ 9,028	$ 197,347	$ (14,023)		$ 192,352
BALANCE (in shares) at Sep. 28, 2019		7,707,886				7,707,886