Computation of Basic and Diluted Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 26, 2014	Sep. 27, 2013	Sep. 26, 2014	Sep. 27, 2013
Numerators:
Income from continuing operations	$ 5,119	$ 2,244	$ 11,381	$ 5,278
Consolidated loss from discontinued operations	(594)	(466)	(5,138)	(2,235)
Less: income (loss) attributable to noncontrolling interest		12	(10)	(42)
Loss from discontinued operations attributable to GSI Group Inc.	(594)	(454)	(5,148)	(2,277)
Net income attributable to GSI Group Inc.	$ 4,525	$ 1,790	$ 6,233	$ 3,001
Denominators:
Weighted average common shares outstanding—basic	34,389	34,102	34,333	34,058
Dilutive potential common shares	404	315	392	267
Weighted average common shares outstanding— diluted	34,793	34,417	34,725	34,325
Antidilutive common shares excluded from above		37	29	327
Basic Earnings (Loss) per Common Share:
From continuing operations	$ 0.15	$ 0.07	$ 0.33	$ 0.15
From discontinued operations	$ (0.02)	$ (0.02)	$ (0.15)	$ (0.07)
Basic earnings per share attributable to GSI Group Inc.	$ 0.13	$ 0.05	$ 0.18	$ 0.08
Diluted Earnings (Loss) per Common Share:
From continuing operations	$ 0.15	$ 0.07	$ 0.33	$ 0.15
From discontinued operations	$ (0.02)	$ (0.02)	$ (0.15)	$ (0.07)
Diluted earnings per share attributable to GSI Group Inc.	$ 0.13	$ 0.05	$ 0.18	$ 0.08