Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Oct. 02, 2015	Jul. 03, 2015	Apr. 03, 2015	Dec. 31, 2014	Sep. 26, 2014	Jun. 27, 2014	Mar. 28, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 90,219	$ 92,271	$ 96,494	$ 94,614	$ 94,012	$ 94,656	$ 96,905	$ 79,133	$ 373,598	$ 364,706	$ 316,910
Cost of revenue	53,590	52,361	55,149	54,608	54,284	54,973	58,254	47,028	215,708	214,539	184,683
Gross profit	36,629	39,910	41,345	40,006	39,728	39,683	38,651	32,105	157,890	150,167	132,227
Operating expenses:
Research and development and engineering	7,295	7,693	7,840	8,215	7,837	7,735	7,525	5,857	31,043	28,954	23,787
Selling, general and administrative	19,080	19,979	20,922	22,068	21,840	21,512	21,410	19,618	82,049	84,380	76,337
Amortization expense – operating expenses	2,018	1,852	1,852	1,889	2,799	2,843	2,876	1,744	7,611	10,262	7,270
Restructuring, acquisition and divestiture related costs	4,022	1,379	416	2,437	(14)	771	360	818
Total operating expenses	32,415	30,903	31,030	34,609	73,904	32,861	32,171	28,037	128,957	166,973	112,781
Impairment of goodwill and intangible assets					41,442					41,442
Operating income (loss) from continuing operations	4,214	9,007	10,315	5,397	(34,176)	6,822	6,480	4,068	28,933	(16,806)	19,446
Interest income (expense), foreign exchange transaction gains (losses), other income (expense), net and gain on disposal of business	1,721	13	15,506	(151)	(127)	310	(1,017)	(275)
Income (loss) from continuing operations before income taxes	5,935	9,020	25,821	5,246	(34,303)	7,132	5,463	3,793	46,022	(17,915)	16,177
Income tax provision (benefit)	(168)	2,452	6,310	1,800	(6,013)	2,013	2,057	937	10,394	(1,006)	6,200
Income (loss) from continuing operations	6,103	6,568	19,511	3,446	(28,290)	5,119	3,406	2,856	35,628	(16,909)	9,977
Loss from discontinued operations, net of tax			(13)		(790)	(273)	(2,678)	(1,866)	(13)	(5,607)	(2,054)
Loss on disposal of discontinued operations, net of tax					(1,405)	(321)				(1,726)	(592)
Consolidated net income (loss)	$ 6,103	$ 6,568	$ 19,498	$ 3,446	(30,485)	4,525	728	990	35,615	(24,242)	7,331
Less: income attributable to noncontrolling interest							(3)	(7)		(10)	(22)
Net income (loss) attributable to GSI Group Inc.					$ (30,485)	$ 4,525	$ 725	$ 983	$ 35,615	$ (24,252)	$ 7,309
Earnings (loss) per common share from continuing operations:
Basic	$ 0.18	$ 0.19	$ 0.56	$ 0.10	$ (0.82)	$ 0.15	$ 0.10	$ 0.08	$ 1.03	$ (0.49)	$ 0.29
Diluted	0.18	0.19	0.56	0.10	(0.82)	0.15	0.10	0.08	1.02	(0.49)	0.29
Loss per common share from discontinued operations:
Basic			0.00		(0.06)	(0.02)	(0.08)	(0.05)	0.00	(0.21)	(0.08)
Diluted			0.00		(0.06)	(0.02)	(0.08)	(0.05)	0.00	(0.21)	(0.08)
Earnings (loss) per common share attributable to GSI Group Inc.:
Basic	0.18	0.19	0.56	0.10	(0.88)	0.13	0.02	0.03	1.03	(0.70)	0.21
Diluted	$ 0.18	$ 0.19	$ 0.56	$ 0.10	$ (0.88)	$ 0.13	$ 0.02	$ 0.03	$ 1.02	$ (0.70)	$ 0.21