Quarterly Financial Information (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 27, 2013	Jun. 28, 2013	Mar. 29, 2013	Dec. 31, 2012	Sep. 28, 2012	Jun. 29, 2012	Mar. 30, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Quarterly Financial Information [Line Items]
Sales	$ 87,707	$ 85,484	$ 85,307	$ 83,114	$ 66,413	$ 69,520	$ 70,379	$ 65,186	$ 341,612	$ 271,498	$ 304,296
Cost of goods sold	51,711	49,693	50,808	49,951	39,138	40,667	39,712	37,505	202,163	157,022	171,196
Gross profit	35,996	35,791	34,499	33,163	27,275	28,853	30,667	27,681	139,449	114,476	133,100
Operating expenses	29,319	30,073	30,152	32,214	23,978	25,061	25,570	24,860	121,758	99,469	97,252
Income from operations	6,677	5,718	4,347	949	3,297	3,792	5,097	2,821	17,691	15,007	35,848
Interest income (expense) and other income (expense), net	(847)	(1,936)	(1,048)	670	(772)	(1,174)	(13)	(1,514)	(3,455)	(2,788)	(12,977)
Income from continuing operations before income taxes	5,830	3,782	3,299	1,619	2,525	2,618	5,084	1,307	14,530	11,534	24,220
Income tax provision (benefit)	1,463	1,610	2,457	150	(12,350)	563	617	230	5,680	(10,940)	2,544
Income from continuing operations	4,367	2,172	842	1,469	14,875	2,055	4,467	1,077	8,850	22,474	21,676
Income (loss) from discontinued operations, net of tax	(79)	(113)	(1,384)	649	(1,317)	(4,570)	414	322
Gain (loss) on disposal of discontinued operations, net of tax		(281)	(311)		2,255				(592)	2,255
Consolidated net income	4,288	1,778	(853)	2,118	15,813	(2,515)	4,881	1,399	7,331	19,578	29,001
Less: Net income attributable to noncontrolling interest	20	12	(18)	(36)	5	(19)	(8)	(18)	(22)	(40)	(28)
Net income (loss) attributable to GSI Group Inc.	$ 4,308	$ 1,790	$ (871)	$ 2,082	$ 15,818	$ (2,534)	$ 4,873	$ 1,381	$ 7,309	$ 19,538	$ 28,973
Earnings from continuing operations per common share:
Basic	$ 0.13	$ 0.06	$ 0.02	$ 0.04	$ 0.44	$ 0.06	$ 0.13	$ 0.03	$ 0.26	$ 0.66	$ 0.65
Diluted	$ 0.13	$ 0.06	$ 0.02	$ 0.04	$ 0.44	$ 0.06	$ 0.13	$ 0.03	$ 0.26	$ 0.66	$ 0.64
Earnings (loss) from discontinued operations per common share:
Basic		$ (0.01)	$ (0.05)	$ 0.02	$ 0.03	$ (0.13)	$ 0.01	$ 0.01	$ (0.05)	$ (0.08)	$ 0.22
Diluted		$ (0.01)	$ (0.05)	$ 0.02	$ 0.03	$ (0.13)	$ 0.01	$ 0.01	$ (0.05)	$ (0.08)	$ 0.22
Net income (loss) per common share:
Basic	$ 0.13	$ 0.05	$ (0.03)	$ 0.06	$ 0.47	$ (0.07)	$ 0.14	$ 0.04	$ 0.21	$ 0.58	$ 0.87
Diluted	$ 0.13	$ 0.05	$ (0.03)	$ 0.06	$ 0.47	$ (0.07)	$ 0.14	$ 0.04	$ 0.21	$ 0.58	$ 0.86