CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 03, 2015	Jun. 27, 2014	Jul. 03, 2015	Jun. 27, 2014
Income Statement [Abstract]
Revenue	$ 96,494	$ 96,905	$ 191,108	$ 176,038
Cost of revenue	55,149	58,254	109,757	105,282
Gross profit	41,345	38,651	81,351	70,756
Operating expenses:
Research and development and engineering	7,840	7,525	16,055	13,382
Selling, general and administrative	20,922	21,410	42,990	41,028
Amortization of purchased intangible assets	1,852	2,876	3,741	4,620
Restructuring, acquisition and divestiture related costs	416	360	2,853	1,178
Total operating expenses	31,030	32,171	65,639	60,208
Operating income from continuing operations	10,315	6,480	15,712	10,548
Interest income (expense), net	(1,375)	(1,375)	(2,772)	(2,212)
Foreign exchange transaction gains (losses), net	(3,153)	(61)	(2,636)	(80)
Other income (expense), net	20,034	419	20,763	1,000
Income from continuing operations before income taxes	25,821	5,463	31,067	9,256
Income tax provision	6,310	2,057	8,110	2,994
Income from continuing operations	19,511	3,406	22,957	6,262
Loss from discontinued operations, net of tax	(13)	(2,678)	(13)	(4,544)
Consolidated net income	19,498	728	22,944	1,718
Less: Net income attributable to noncontrolling interest		(3)		(10)
Net income attributable to GSI Group Inc.	$ 19,498	$ 725	$ 22,944	$ 1,708
Earnings per common share from continuing operations:
Basic	$ 0.56	$ 0.10	$ 0.66	$ 0.18
Diluted	0.56	0.10	0.66	0.18
Loss per common share from discontinued operations:
Basic	0.00	(0.08)	0.00	(0.13)
Diluted	0.00	(0.08)	0.00	(0.13)
Earnings per common share attributable to GSI Group Inc.:
Basic	0.56	0.02	0.66	0.05
Diluted	$ 0.56	$ 0.02	$ 0.66	$ 0.05
Weighted average common shares outstanding—basic	34,630	34,378	34,567	34,304
Weighted average common shares outstanding—diluted	35,029	34,707	35,014	34,690