CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 02, 2015	Sep. 26, 2014	Oct. 02, 2015	Sep. 26, 2014
Income Statement [Abstract]
Revenue	$ 92,271	$ 94,656	$ 283,379	$ 270,694
Cost of revenue	52,361	54,973	162,118	160,255
Gross profit	39,910	39,683	121,261	110,439
Operating expenses:
Research and development and engineering	7,693	7,735	23,748	21,117
Selling, general and administrative	19,979	21,512	62,969	62,540
Amortization of purchased intangible assets	1,852	2,843	5,593	7,463
Restructuring, acquisition and divestiture related costs	1,379	771	4,232	1,949
Total operating expenses	30,903	32,861	96,542	93,069
Operating income from continuing operations	9,007	6,822	24,719	17,370
Interest income (expense), net	(1,248)	(1,453)	(4,020)	(3,665)
Foreign exchange transaction gains (losses), net	383	1,030	(2,253)	950
Other income (expense), net	878	733	21,641	1,733
Income from continuing operations before income taxes	9,020	7,132	40,087	16,388
Income tax provision	2,452	2,013	10,562	5,007
Income from continuing operations	6,568	5,119	29,525	11,381
Loss from discontinued operations, net of tax		(273)	(13)	(4,817)
Loss on disposal of discontinued operations, net of tax		(321)		(321)
Consolidated net income	6,568	4,525	29,512	6,243
Less: Net income attributable to noncontrolling interest				(10)
Net income attributable to GSI Group Inc.	$ 6,568	$ 4,525	$ 29,512	$ 6,233
Earnings per common share from continuing operations:
Basic	$ 0.19	$ 0.15	$ 0.85	$ 0.33
Diluted	0.19	0.15	0.84	0.33
Loss per common share from discontinued operations:
Basic		(0.02)	0.00	(0.15)
Diluted		(0.02)	0.00	(0.15)
Earnings per common share attributable to GSI Group Inc.:
Basic	0.19	0.13	0.85	0.18
Diluted	$ 0.19	$ 0.13	$ 0.84	$ 0.18
Weighted average common shares outstanding—basic	34,599	34,389	34,578	34,333
Weighted average common shares outstanding—diluted	35,055	34,793	35,027	34,725