Computation of Basic and Diluted Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
Apr. 03, 2015	Mar. 28, 2014
Numerators:
Income from continuing operations	$ 3,446	$ 2,856
Consolidated loss from discontinued operations		(1,866)
Less: Income attributable to noncontrolling interest		(7)
Loss from discontinued operations attributable to GSI Group Inc.		(1,873)
Net income attributable to GSI Group Inc.	$ 3,446us-gaap_NetIncomeLoss	$ 983us-gaap_NetIncomeLoss
Denominators:
Weighted average common shares outstanding—basic	34,506	34,227
Dilutive potential common shares	493	442
Weighted average common shares outstanding— diluted	34,999	34,669
Antidilutive common shares excluded from above		87
Basic Earnings (Loss) per Common Share:
From continuing operations	$ 0.10	$ 0.08
From discontinued operations		$ (0.05)
Basic earnings per share attributable to GSI Group Inc.	$ 0.10us-gaap_EarningsPerShareBasic	$ 0.03us-gaap_EarningsPerShareBasic
Diluted Earnings (Loss) per Common Share:
From continuing operations	$ 0.10	$ 0.08
From discontinued operations		$ (0.05)
Diluted earnings per share attributable to GSI Group Inc.	$ 0.10us-gaap_EarningsPerShareDiluted	$ 0.03us-gaap_EarningsPerShareDiluted

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