CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statement [Abstract]
Revenue	$ 373,598	$ 364,706	$ 316,910
Cost of revenue	215,708	214,539	184,683
Gross profit	157,890	150,167	132,227
Operating expenses:
Research and development and engineering	31,043	28,954	23,787
Selling, general and administrative	82,049	84,380	76,337
Amortization of purchased intangible assets	7,611	10,262	7,270
Restructuring, acquisition and divestiture related costs	8,254	1,935	5,387
Impairment of goodwill and intangible assets		41,442
Total operating expenses	128,957	166,973	112,781
Operating income (loss) from continuing operations	28,933	(16,806)	19,446
Interest income (expense), net	(5,180)	(5,096)	(3,468)
Foreign exchange transaction gains (losses), net	(23)	1,281	(1,301)
Other income (expense), net	2,663	2,706	1,500
Gain on disposal of business	19,629
Income (loss) from continuing operations before income taxes	46,022	(17,915)	16,177
Income tax provision (benefit)	10,394	(1,006)	6,200
Income (loss) from continuing operations	35,628	(16,909)	9,977
Loss from discontinued operations, net of tax	(13)	(5,607)	(2,054)
Loss on disposal of discontinued operations, net of tax		(1,726)	(592)
Consolidated net income (loss)	35,615	(24,242)	7,331
Less: Net income attributable to noncontrolling interest		(10)	(22)
Net income (loss) attributable to GSI Group Inc.	$ 35,615	$ (24,252)	$ 7,309
Earnings (loss) per common share from continuing operations:
Basic	$ 1.03	$ (0.49)	$ 0.29
Diluted	1.02	(0.49)	0.29
Loss per common share from discontinued operations:
Basic	0.00	(0.21)	(0.08)
Diluted	0.00	(0.21)	(0.08)
Earnings (loss) per common share attributable to GSI Group Inc.:
Basic	1.03	(0.70)	0.21
Diluted	$ 1.02	$ (0.70)	$ 0.21
Weighted average common shares outstanding—basic	34,579	34,352	34,073
Weighted average common shares outstanding—diluted	34,827	34,352	34,396
Amounts attributable to GSI Group Inc.:
Income (loss) from continuing operations	$ 35,628	$ (16,909)	$ 9,977
Loss from discontinued operations	(13)	(7,343)	(2,668)
Net income (loss) attributable to GSI Group Inc.	$ 35,615	$ (24,252)	$ 7,309