Computation of Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 28, 2014	Mar. 29, 2013
Numerators:
Consolidated net income	$ 2,856	$ 1,749
Less: income attributable to noncontrolling interest	(7)	(36)
Income from continuing operations	2,849	1,713
Income (loss) from discontinued operations	(1,866)	369
Net income attributable to GSI Group Inc.	$ 983	$ 2,082
Denominators:
Weighted average common shares outstanding-basic	34,227	33,983
Dilutive potential common shares	442	288
Weighted average common shares outstanding-diluted	34,669	34,271
Antidilutive common shares excluded from above	87	373
Basic Earnings (Loss) per Common Share:
From continuing operations	$ 0.08	$ 0.05
From discontinued operations	$ (0.05)	$ 0.01
Basic earnings (loss) per share attributable to GSI Group Inc.	$ 0.03	$ 0.06
Diluted Earnings (Loss) per Common Share:
From continuing operations	$ 0.08	$ 0.05
From discontinued operations	$ (0.05)	$ 0.01
Diluted earnings (loss) per share attributable to GSI Group Inc.	$ 0.03	$ 0.06