Computation of Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 27, 2014	Jun. 28, 2013	Jun. 27, 2014	Jun. 28, 2013
Numerators:
Income from continuing operations	$ 3,406	$ 1,285	$ 6,262	$ 3,034
Consolidated income (loss) from discontinued operations	(2,678)	(2,138)	(4,544)	(1,769)
Less: income attributable to noncontrolling interest	(3)	(18)	(10)	(54)
Consolidated income (loss) from discontinued operations	(2,681)	(2,156)	(4,554)	(1,823)
Net income (loss) attributable to GSI Group Inc.	$ 725	$ (871)	$ 1,708	$ 1,211
Denominators:
Weighted average common shares outstanding-basic	34,378	34,088	34,304	34,036
Dilutive potential common shares	329	197	386	243
Weighted average common shares outstanding-diluted	34,707	34,285	34,690	34,279
Antidilutive common shares excluded from above		570	44	472
Basic Earnings (Loss) per Common Share:
From continuing operations	$ 0.10	$ 0.03	$ 0.18	$ 0.08
From discontinued operations	$ (0.08)	$ (0.06)	$ (0.13)	$ (0.05)
Basic earnings (loss) per share attributable to GSI Group Inc.	$ 0.02	$ (0.03)	$ 0.05	$ 0.03
Diluted Earnings (Loss) per Common Share:
From continuing operations	$ 0.10	$ 0.03	$ 0.18	$ 0.08
From discontinued operations	$ (0.08)	$ (0.06)	$ (0.13)	$ (0.05)
Diluted earnings (loss) per share attributable to GSI Group Inc.	$ 0.02	$ (0.03)	$ 0.05	$ 0.03